Variable compression ratio device

Disclosed is a variable compression ratio device which changes a top dead center of a piston provided in an engine depending on a driving state of the engine. The variable compression ratio device may include: a lower piston reciprocally movable in a cylinder of the engine and connected with a connecting rod to rotate a crankshaft, an operation chamber, an upper piston disposed above the lower piston and partially inserted into the operation chamber, a push plate dividing the operation chamber into upper and lower spaces, a hydraulic pressure chamber which is the lower space, an elastic member provided in the upper space to push the push plate downward, a hydraulic pressure supply unit selectively supplying hydraulic pressure to the hydraulic pressure chamber, and a hydraulic pressure supply pathway connecting the hydraulic pressure supply unit and the hydraulic pressure chamber for supplying the hydraulic pressure.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent Application Number 10-2013-0155934 filed on Dec. 13, 2013, the entire contents of which application are incorporated herein for all purposes by this reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a variable compression ratio device, and more particularly, to a variable compression ratio device that changes a compression ratio by changing a volume of a combustion chamber.

2. Description of Related Art

In general, thermal efficiency of a heat engine increases as a compression ratio becomes higher. Here, the compression ratio is a ratio of a volume when gas flowing into a cylinder is compressed by a piston, and is represented by ‘a cylinder volume/a combustion chamber volume at a top dead center of a piston’. That is, the compression ratio increases as the top dead center of the piston becomes higher.

In the case of a spark ignition engine, thermal efficiency may be increased by advancing ignition timing, but there may be a limit in advancing the ignition timing when considering abnormal combustion. Therefore, there is a need for a variable compression ratio (VCR) device for improving thermal efficiency of the heat engine.

The variable compression ratio device is a device that changes a compression ratio of a gaseous mixture depending on a driving state of the engine. The variable compression ratio device improves fuel efficiency by raising a compression ratio of a gaseous mixture at a low load driving state (low load condition) of the engine. At a high load driving state (high load condition) of the engine, the variable compression ratio device serves to prevent the occurrence of knocking and improve engine output by maximally supplying the gaseous mixture, and simultaneously lowering the compression ratio of the gaseous mixture.

In the variable compression ratio device, a manner of moving a cylinder block, a manner of changing a volume of the combustion chamber, a manner of changing the top dead center of the piston, and the like are applied.

However, numerous mechanical constituent elements are required in order to implement the variable compression ratio device in the related art, and thus the configuration of the variable compression ratio device may be complicated. In addition, in a case in which a motor or the like, which uses electricity as a power source, is used to drive the mechanical constituent elements, there is a problem in that fuel efficiency may deteriorate.

Furthermore, since power transmission of the motor requires relatively larger drive torque than other gear engagement, there is a limit in that a capacity of the motor becomes small. Therefore, an overall weight of the vehicle may be increased, and fuel efficiency may deteriorate.

Meanwhile, since connection relationships between the mechanical constituent elements are complicated, it is difficult to ensure quick responsiveness of the variable compression ratio device.

SUMMARY OF INVENTION

The present invention has been made in an effort to provide a variable compression ratio device which improves fuel efficiency. In addition, the present invention has been made in an effort to provide a variable compression ratio device which may have a simplified configuration, and may ensure responsiveness.

Various aspects of the present invention provide a variable compression ratio device which changes a top dead center of a piston provided in an engine depending on a driving state of the engine. The variable compression ratio device may include: a lower piston which is provided to be reciprocally movable in a cylinder of the engine, and connected with a connecting rod to rotate a crankshaft by reciprocal motion thereof; an operation chamber that is formed above a portion of the lower piston which is connected with the connecting rod; an upper piston which is disposed above the lower piston, and partially inserted into the operation chamber; a push plate which is formed on a part of the upper piston to divide the operation chamber into an upper space and a lower space; a hydraulic pressure chamber which is the lower space of the divided operation chamber; an elastic member which is provided in the upper space of the divided operation chamber to push the push plate downward; a hydraulic pressure supply unit which selectively supplies hydraulic pressure to the hydraulic pressure chamber; and a hydraulic pressure supply pathway which connects the hydraulic pressure supply unit and the hydraulic pressure chamber so that the hydraulic pressure is supplied from the hydraulic pressure supply unit to the hydraulic pressure chamber.

When the hydraulic pressure supplied to the hydraulic pressure chamber is equal to or more than a predetermined amount, the upper piston may be moved upward with respect to the lower piston. When the hydraulic pressure supplied to the hydraulic pressure chamber is less than the predetermined amount, the upper piston may be moved to an original position to come into contact with the lower piston as the push plate is pushed by the elastic member.

The hydraulic pressure supply pathway may include: a first hydraulic pressure line which is formed in a cylinder block, and has one end connected with the hydraulic pressure supply unit; a second hydraulic pressure line which is formed in the crankshaft, and has one end that communicates with the other end of the first hydraulic pressure line; a third hydraulic pressure line which is formed in the connecting rod, and has one end that communicates with the other end of the second hydraulic pressure line; and a fourth hydraulic pressure line which is formed in the lower piston, and has one end that communicates with the other end of the third hydraulic pressure line, and the other end that communicates with the hydraulic pressure chamber.

Fluid supplied from the hydraulic pressure supply unit may be supplied to the hydraulic pressure chamber sequentially through the first hydraulic pressure line, the second hydraulic pressure line, the third hydraulic pressure line, and the fourth hydraulic pressure line.

A connection portion between the first hydraulic pressure line and the second hydraulic pressure line, and a connection portion between the second hydraulic pressure line and the third hydraulic pressure line may be formed in a substantially circular groove shape to prevent loss of fluid due to rotation of the crankshaft.

Sealing members may be provided at the connection portions between the first hydraulic pressure line and the second hydraulic pressure line, and between the second hydraulic pressure line and the third hydraulic pressure line, and at a connection portion between the third hydraulic pressure line and the fourth hydraulic pressure line, respectively. The sealing members, which are provided at the connection portions between the first hydraulic pressure line and the second hydraulic pressure line, and between the second hydraulic pressure line and the third hydraulic pressure line, respectively, may be formed to have a shape that corresponds to the substantially circular groove shape of the connection portions.

Sealing members may be provided at a hydraulic pressure supply pathway connection portion between the lower piston and the connecting rod, a hydraulic pressure supply pathway connection portion between the connecting rod and the crankshaft, and a hydraulic pressure supply pathway connection portion between the crankshaft and the cylinder block.

The variable compression ratio device may further include a valve which is disposed between the hydraulic pressure supply unit and the hydraulic pressure supply pathway, and selectively opened or closed so that the hydraulic pressure is selectively supplied to the hydraulic pressure chamber. The valve may adjust an amount of fluid that is supplied to the hydraulic pressure chamber.

DETAILED DESCRIPTION

FIG. 1is a configuration diagram of a variable compression ratio device according to various embodiments of the present invention. As illustrated inFIG. 1, a variable compression ratio device according to various embodiments of the present invention includes a lower piston10, an upper piston20, an elastic member26, a hydraulic pressure supply circuit or pathway40, and a hydraulic pressure supply unit70. In addition, the lower piston10, the upper piston20, and the elastic member26constitute a piston P that is provided to be reciprocally movable in a cylinder C of an engine.

The lower piston10is connected with a connecting rod30so as to rotate a crankshaft50by the reciprocal motion of the piston in the cylinder C (seeFIG. 3). In addition, the lower piston10includes a pin hole12, an operation chamber14, a hydraulic pressure chamber16, and a rod insertion hole18.

The connecting rod30receives combustion force from the lower piston10, and transmits the combustion force to the crankshaft50(seeFIG. 3). In order to transmit the combustion force, one end of the connecting rod30is rotatably connected to the lower piston10by a piston pin35, and the other end of the connecting rod30is rotatably connected to the crankshaft50. Typically, the one end of the connecting rod30which is connected with the piston P is called a small end32, and the other end of the connecting rod30which is connected with the crankshaft50is called a big end34.

The pin hole12is a hole into which the piston pin35is inserted. That is, the piston pin35is disposed to pass through the small end32of the connecting rod30and the pin hole12, such that the connecting rod30and the lower piston10are connected.

The connection between the connecting rod30and the piston P using the piston pin35may be the same as or similar to those in the art, and thus more detailed description thereof will be omitted.

The operation chamber14is a space that is formed in the lower piston10relatively above a portion where the connecting rod30and the lower piston10are connected. The hydraulic pressure chamber16is formed so that hydraulic pressure may be supplied to a part of the operation chamber14. The rod insertion hole18is a hole that is pierced from an upper end of the lower piston10to the operation chamber14.

A part of the upper piston20is inserted into the rod insertion hole18so as to be connected with the lower piston10, and disposed relatively above the lower piston10. In addition, the lower piston10and the upper piston20are inserted into the cylinder C with almost no clearance from an inner wall of the cylinder C. Meanwhile, in order to maintain air-tightness between the lower piston10and the upper piston20and the inner wall of the cylinder C, piston rings may be provided on the lower piston10and the upper piston20depending on a design of those skilled in the art. Furthermore, the upper piston20is provided to be selectively movable upward and downward on the basis of the lower piston10. Here, as a volume of a combustion chamber1is changed by the upward and downward motion of the upper piston20, a compression ratio of a gaseous mixture is changed.

The combustion chamber1is a space that is formed between the piston P and the cylinder C, and the gaseous mixture is sucked into the combustion chamber1, or combusted gas is discharged from the combustion chamber1, depending on opening and closing operations of an intake valve3and an exhaust valve5. The combustion chamber1, and the opening and closing operations of the intake and exhaust valves3and5may be the same as or similar to those in the art, and thus detailed description thereof will be omitted. In various embodiments of the present invention, the combustion chamber1is formed between the upper piston20and the cylinder C.

The upper piston20includes a connection rod22, and a push plate24. The connection rod22is a part of the upper piston20which is inserted into the rod insertion hole18. That is, the connection rod22is formed on a lower portion of the upper piston20, and one end of the connection rod22is inserted up to the operation chamber14through the rod insertion hole18.

The push plate24is formed on the one end of the connection rod22which is inserted into the rod insertion hole18. In addition, the push plate24is formed in a wide plate shape. Furthermore, the push plate24is provided with almost no clearance from an inner wall of the operation chamber14, and the operation chamber14is divided into an upper space and a lower space by the push plate24. Here, the hydraulic pressure chamber16is the lower space among the upper and lower spaces of the operation chamber14that is divided by the push plate24.

The elastic member26is disposed in the upper space of the operation chamber14. In addition, the elastic member26is provided to push the push plate24downward. Meanwhile, the elastic member26may be a coil spring, but the present invention is not limited thereto.

The hydraulic pressure supply circuit or pathway40is formed and disposed to supply hydraulic pressure to the hydraulic pressure chamber16. A configuration in which the hydraulic pressure supply circuits40are formed in the connecting rod30and the lower piston10, respectively, is illustrated inFIG. 1. Here, the hydraulic pressure supply circuit40formed in the connecting rod30communicates with the hydraulic pressure supply circuit40formed in the lower piston10, and the hydraulic pressure supply circuit40formed in the lower piston10communicates with the hydraulic pressure chamber16.

The hydraulic pressure supply unit70is a device that supplies hydraulic pressure to the hydraulic pressure supply circuit40. In addition, hydraulic pressure supplied from the hydraulic pressure supply unit70is supplied to the hydraulic pressure chamber16sequentially through the hydraulic pressure supply circuit40formed in the connecting rod30and the hydraulic pressure supply circuit40formed in the lower piston10. Meanwhile, the hydraulic pressure supply unit70may be a typical oil pump, but the present invention is not limited thereto, and fluid, which forms hydraulic pressure that is supplied to the hydraulic pressure chamber16through the hydraulic pressure supply circuit or pathway40, may be oil or gas.

The hydraulic pressure supply unit70includes a supply valve72. The supply valve72is opened or closed so that hydraulic pressure is selectively supplied, and interposed between the hydraulic pressure supply unit70and the hydraulic pressure supply circuit40. In addition, the supply valve72adjusts a feed rate of the fluid F. However, the present invention is not limited thereto, and the supply valve72may not be needed in a case in which the hydraulic pressure supply unit70is operated to selectively supply hydraulic pressure.

FIGS. 2A and 2Billustrate operation of an variable compression ratio device according to various embodiments of the present invention. As illustrated inFIG. 2, the upper piston20is moved upward and downward on the basis of the lower piston10depending on an amount of the fluid F that is injected into the hydraulic pressure chamber16. Here, an amount of the fluid F represents the hydraulic pressure or the intensity of the hydraulic pressure.

FIG. 2Aillustrates a state in which the upper piston20is moved downward when the supply of hydraulic pressure to the hydraulic pressure chamber16is shut off or a small amount of fluid F is supplied to the hydraulic pressure chamber16, andFIG. 2Billustrates a state in which the upper piston20is moved upward when a predetermined amount or more of hydraulic pressure is supplied into the hydraulic pressure chamber16.

As illustrated inFIG. 2A, in a case in which the supply of hydraulic pressure from the hydraulic pressure supply unit70to the hydraulic pressure chamber16is shut off or a small amount of fluid F is supplied to the hydraulic pressure chamber16, the upper piston20is moved downward by force by which the elastic member26pushes the push plate24. In addition, a lower surface of the upper piston20on which the connection rod22protrudes comes into contact with an upper surface of the lower piston10. Therefore, the volume of the combustion chamber1is increased.

As illustrated inFIG. 2B, in a case in which a predetermined amount or more of hydraulic pressure is supplied from the hydraulic pressure supply unit70to the hydraulic pressure chamber16, the upper piston20is moved upward by force by which the fluid F pushes the push plate24. That is, the lower surface of the upper piston20on which the connection rod22protrudes is moved to be spaced apart from the upper surface of the lower piston10. Therefore, the volume of the combustion chamber1is decreased. Here, a set value of the hydraulic pressure may be set by those skilled in the art by taking elastic force of the elastic member26into consideration.

FIG. 3is a view schematically illustrating the hydraulic pressure supply circuit or pathway according to various embodiments of the present invention. As illustrated inFIG. 3, the hydraulic pressure supply circuit or pathway40includes first, second, third, and fourth hydraulic pressure lines41,43,45, and47, and first, second, and third lubrication lines42,44, and46.

The first hydraulic pressure line41is formed in a cylinder block60. In addition, one end of the first hydraulic pressure line41is connected with the hydraulic pressure supply unit70.

The second hydraulic pressure line43is formed in the crankshaft50. In addition, one end of the second hydraulic pressure line43communicates with the other end of the first hydraulic pressure line41.

The third hydraulic pressure line45is the hydraulic pressure supply circuit40that is formed in the connecting rod30(seeFIG. 1). In addition, one end of the third hydraulic pressure line45communicates with the other end of the second hydraulic pressure line43. Furthermore, the one end of the third hydraulic pressure line45is formed in the big end34of the connecting rod30, and the other end of the third hydraulic pressure line45is extended toward the small end32along the connecting rod30.

The fourth hydraulic pressure line47is the hydraulic pressure supply circuit40that is formed in the lower piston50(seeFIG. 1). In addition, one end of the fourth hydraulic pressure line47communicates with the other end of the third hydraulic pressure line45that is extended to the small end of the connecting rod30(seeFIG. 1). As described above, the other end of the fourth hydraulic pressure line47communicates with the hydraulic pressure chamber16.

The fluid F supplied from the hydraulic pressure supply unit70is supplied to the hydraulic pressure chamber16sequentially through the first hydraulic pressure line41, the second hydraulic pressure line43, the third hydraulic pressure line45, and the fourth hydraulic pressure line47.

The first, second, and third lubrication lines42,44, and46are provided to supply oil for lubricating a bearing38interposed in a connection portion between the connecting rod30and the crankshaft50, and a bearing58interposed in a connection portion between the cylinder block60and the crankshaft50. That is, the oil, which is supplied through the first, second, and third lubrication lines42,44, and46, allows the crankshaft50to be smoothly rotated.

The first lubrication line42is formed in the cylinder block60. In addition, one end of the first lubrication line42may be connected with the hydraulic pressure supply unit7. A configuration in which the one end of the first lubrication line42is connected with the hydraulic pressure supply unit70is illustrated inFIG. 3, but the present invention is not limited thereto. In other words, in a case in which the fluid F, which is supplied to the hydraulic pressure supply unit70and forms hydraulic pressure, is not oil but gas, the first lubrication line42is not connected with the hydraulic pressure supply unit70, but is connected with a device such as a hydraulic pump for supplying oil.

The second lubrication line44is formed in the crankshaft50. In addition, the second lubrication line44is formed at a portion where the crankshaft50is connected with the cylinder block60. Furthermore, the second lubrication line44is connected with the other end of the first lubrication line42which is extended to the connection portion between the crankshaft50and the cylinder block60. Meanwhile, the second lubrication line44may be formed to penetrate the crankshaft50in a diameter direction of the bearing58. Therefore, oil passing through the first lubrication line42and the second lubrication line44is used to lubricate the bearing58interposed in the connection portion between the cylinder block60and the crankshaft50.

The third lubrication line46is formed in the crankshaft50, and branches off from the second lubrication line44. That is, one end of the third lubrication line46is connected with the second lubrication line44. In addition, the other end of the third lubrication line46is extended to the connection portion between the crankshaft50and the connecting rod30. Therefore, oil passing through the third lubrication line46is used to lubricate the bearing38interposed in the connection portion between the connecting rod30and the crankshaft50.

Oil supplied to the first lubrication line42sequentially passes through the first lubrication line42, the second lubrication line44, and the third lubrication line46, and in this process, oil, which has been used to lubricate the bearings38and58, falls and is collected in the oil pan.

Meanwhile, in order to prevent loss of the fluid F, sealing members80are provided at a hydraulic pressure supply pathway40connection portion between the lower piston10and the connecting rod30, a hydraulic pressure supply pathway40connection portion between the connecting rod30and the crankshaft50, and a hydraulic pressure supply pathway40connection portion between the crankshaft50and the cylinder block60. That is, the sealing members80are interposed between the first hydraulic pressure line41and the second hydraulic pressure line43, between the second hydraulic pressure line43and the third hydraulic pressure line45, and between the third hydraulic pressure line45and the fourth hydraulic pressure line47. Here, in order to prevent loss of the fluid F due to rotation of the crankshaft50, the connection portion between the first hydraulic pressure line41and the second hydraulic pressure line43, and the connection portion between the second hydraulic pressure line43and the third hydraulic pressure line45are formed in a circular groove shape, respectively. In addition, the sealing members80, which are disposed at the connection portion between the first hydraulic pressure line41and the second hydraulic pressure line43, and the connection portion between the second hydraulic pressure line43and the third hydraulic pressure line45, respectively, are formed in a circular shape so as to correspond to the shapes of the connection portion between the first hydraulic pressure line41and the second hydraulic pressure line43, and the connection portion between the second hydraulic pressure line43and the third hydraulic pressure line45.

The sealing members80protrude from a surface where the hydraulic pressure supply pathway40connection portion between the lower piston10and the connecting rod30is formed, so that the sealing member80provided on the lower piston10and the sealing member80provided on the connecting rod30come into contact with each other in an airtight manner. In this case, at least one of the sealing member80provided on the lower piston10and the sealing member80provided on the connecting rod30protrudes. In addition, the sealing member80protrudes from a surface where the hydraulic pressure supply pathway40connection portion between the connecting rod30and the crankshaft50is formed, so that the sealing member80provided on the connecting rod30and the sealing member80provided on the crankshaft50come into contact with each other in an airtight manner. In this case, at least one of the sealing member80provided on the connecting rod30and the sealing member80provided on the crankshaft50protrudes. Furthermore, the sealing member80protrudes from a surface where the hydraulic pressure supply pathway40connection portion between the crankshaft50and the cylinder block60is formed, so that the sealing member80provided on the crankshaft50and the sealing member80provided on the cylinder block60come into contact with each other in an airtight manner. In this case, at least one of the sealing member80provided on the crankshaft50and the sealing member80provided on the cylinder block60protrudes.

As described above, according to various embodiments of the present invention, a weight of a configuration for changing a top dead center of the piston P may be minimized, and the compression ratio may be efficiently changed, thereby improving fuel efficiency. In addition, since hydraulic pressure is used to perform an operation of changing the top dead center of the piston P, the configuration may be simplified, and responsiveness may be improved.