Variable compression ratio device and internal combustion engine including the same

A variable compression ratio device may include a piston assembly having double pistons of which the volume may be varied, a lifter relatively moving one piston of the double pistons with respect to the other piston of the double pistons, a guide unit engaged with the piston assembly and guiding a movement of the one piston with respect to the other piston, and a locking unit selectively coupling the one piston to the other piston.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2013-0022420 filed on Feb. 28, 2013, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable compression ratio device, and more particularly, to a variable compression ratio device capable of varying a compression ratio by varying a protrusion height of an inner piston which is coupled to an outer piston so as to move in an axial direction, and an internal combustion engine including the same.

2. Description of Related Art

In general, a compression ratio of an internal combustion engine is represented by a ratio of a maximum volume of a combustion chamber before compression to a minimum volume of the combustion chamber after compression during a compression stroke of the internal combustion engine.

When the compression ratio of the internal combustion engine is increased, the output of the internal combustion engine increases. However, when the compression ratio of the internal combustion engine is excessively high, a so-called knocking may occur to reduce the output of the internal combustion engine. Furthermore, the internal combustion engine may be overheated or a valve or piston trouble may occur in the internal combustion engine.

Thus, the compression ratio of the internal combustion engine is set to a specific value within a proper range before a knocking occurs. When the compression ratio is properly varied according to a load of the internal combustion engine, the fuel efficiency and output of the internal combustion engine may be improved. Therefore, various methods for varying the compression ratio of the internal combustion engine have been proposed.

The methods for varying the compression ratio of the internal combustion engine may include methods for varying the volume of a combustion chamber during a compression stroke.

For example, the level of top dead center of the piston may be varied during the compression stroke, or the volume of a secondary combustion chamber provided in a cylinder head may be increased or decreased.

U.S. Pat. No. 7,284,512 has disclosed a double piston structure having an outer piston and an inner piston, and the outer piston varies a compression ratio while moved vertically by a hydraulic actuator.

The variable compression ratio device having the above-described double piston structure requires a structural improvement for response and durability.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a variable compression ratio device capable of reducing the weight and cost thereof through a simplified structure and improving response, operation reliability, and durability, and an internal combustion engine including the same.

In an aspect of the present invention, a variable compression ratio device may include a piston assembly having double pistons of which the volume is varied, a lifter relatively moving one piston of the double pistons with respect to the other piston of the double pistons, a guide unit engaged with the piston assembly and guiding a movement of the one piston with respect to the other piston, and a locking unit selectively coupling the one piston to the other piston.

The double piston may include an outer piston, and an inner piston slidably coupled to the outer piston so as to protrude from the outer piston to the outside of the outer piston.

The outer piston may include an opening formed at a top thereof, and a housing groove formed in the outer piston, wherein the inner piston is inserted through the opening and mounted in the housing groove.

The guide unit may include a pinion gear rotatably mounted on an exterior circumference of the inner piston, and a rack gear mounted in the outer piston so as to be engaged with the pinion gear.

The lifter may include a wax or bimetal which pushes the inner piston upward through the opening in receiving an electrical signal.

The wax or bimetal is formed in a plate shape, and the inner piston is supported by the wax or bimetal.

The locking unit may include a solenoid installed in the outer piston and selectively protruding toward the housing groove in receiving an electrical signal, and a locking groove formed in the inner piston such that the solenoid is selectively coupled to the locking groove to lock the outer piston and the inner piston.

The variable compression ratio device may further include an engine control unit (ECU) detecting an operation state of an engine and applying an electrical signal to the lifter and the locking unit such that the volume of the piston is varied according to the operation state of the engine.

The ECU varies a compression ratio by controlling a magnitude of the electrical signal applied to the lifter according to the operation state of the engine.

An internal combustion engine may include a cylinder block having the piston assembly, the piston assembly being housed to reciprocate along the cylinder block, and a cylinder head coupled to the top of the cylinder block and forming a combustion chamber with the cylinder block.

In the variable compression ratio device and the internal combustion engine including the same according to the embodiments of the present invention, as the flexible member is extended in the axial direction of the connecting rod according to the control signal of the ECU, the internal piston is lifted to increase the compression ratio. When the flexible member is contracted in the axial direction of the connecting rod, the inner piston is lowered to decrease the compression ratio.

Thus, the structure may be simplified to reduce the weight and cost of a vehicle and improve the durability and operation reliability.

Furthermore, since the variable compression ratio device is operated according to an electrical signal, the response thereof may be improved. The variable compression ratio device may control the compression ratio according to the operation situation of the engine, thereby improving the output and fuel efficiency of the engine.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, a cylinder head20is mounted over a cylinder block10constituting an engine, thereby forming a combustion chamber.

A piston30is inserted into the cylinder block10so as to reciprocate vertically along the cylinder block10. One end of a connecting rod40is connected to the piston30through a piston pin or the like so as to move as one unit, and the other end of the connecting rod40is coupled to a crankshaft50.

When the piston30reciprocates along the cylinder block10, the connecting rod40converts the reciprocating operation of the piston30into a rotating operation to rotate the crankshaft50, and the crankshaft50generates a rotation power while rotated in one direction.

When the piston30rises or drops along the cylinder block10, the volume of the combustion chamber is varied by the piston30.

When the volume of the combustion chamber formed by the cylinder10, the cylinder head20, and the piston30is varied at the time at which the piston30is moved toward the top of the combustion chamber and positioned at the top dead center, the compression ratio of the engine is varied.

According to the exemplary embodiment of the present invention, when the piston30is positioned at the top dead center, the volume of the piston30may be varied to control the compression ratio of the engine.

That is, the piston30is a volume variable piston.

The volume variable piston30has a double piston structure to vary the volume thereof.

That is, the piston30includes an outer piston32and an inner piston34.

The outer piston32has an opening55formed at the top thereof and a housing groove32aformed therein to communicate with the opening55. The housing groove32ais expanded in a radial direction to have a larger diameter than that of the inner piston34, and extended in an axial direction.

The inner piston34is inserted through the upper opening of the outer piston32and housed in the housing groove32a.

The inner piston34is installed to relatively move in an axial direction with respect to the outer piston32in a state in which the inner piston34is housed in the housing groove32a.

A guide unit is provided between the inner piston34and the outer piston32so as to guide the movement of the inner piston34.

The guide unit includes a pinion gear60mounted on the exterior circumference of the inner piston34positioned in the housing groove32aand a rack gear62mounted on the exterior circumference of the housing groove32afacing the exterior circumference of the inner piston34and engaged with the pinion gear60.

When the inner piston34is relatively moved with respect to the outer piston32, the pinion gear60is moved along the rack gear62in a state where the pinion gear60is engaged with the rack gear62, thereby guiding the movement of the inner piston34.

A lifter70is provided to relatively move the inner piston34with respect to the outer piston32.

The lifter70is installed at the bottom of the inner piston34, and may have a plate shape.

The lifter70may include a bimetal plate or wax plate which is deformed to protrude upward in the axial direction when receiving an electrical signal, and pushes the inner piston34upward in the axial direction toward the combustion chamber.

A locking unit is provided to maintain the position of the inner piston34in a state where the inner piston34is pushed upward by the lifter70.

The locking unit may include a solenoid80installed in the outer piston32so as to protrude toward the housing groove32aand a locking groove34aformed on the exterior circumference of the inner piston34. The locking groove34amay have a depressed shape such that the solenoid80is detachably coupled to the locking groove34a.

InFIG. 2, a low compression ratio state corresponds to a state in which the inner piston34is inserted into the housing groove32aof the outer piston32when the outer piston32is positioned at the top dead center. In this state, the combustion chamber has a volume V1formed by the cylinder head20, the cylinder block10, the outer piston32, and the top surface of the inner piston34.

When an engine control unit (ECU) applies an electrical signal to the lifter70at the time at which the outer piston32is positioned at the top dead center, the lifter70is elastically deformed upward in the axial direction toward the combustion chamber, and the inner piston34supported by the lifter70is protruded from the housing groove32aof the outer piston32upward in the axial direction toward the combustion chamber through the elastic deformation of the lifter70.

Thus, the volume V2of the combustion chamber decreases by a volume (V1-V2) corresponding to the protrusion height H of the inner piston34. Then, a high compression ratio state is realized.

The ECU applies an electrical signal to the solenoid80in a state where the inner piston34is protruded by the lifter70, and the solenoid80is inserted and locked to the locking groove34aof the inner piston34toward the housing groove32, thereby maintaining the high compression ratio state.

When the electrical signal applied by the ECU is blocked, the lifter70and the solenoid80are recovered to the original shapes thereof, and the inner piston34is housed in the housing groove32aby the weight thereof and the pressure of the compression chamber, thereby realizing the low compression ratio state.

According to the magnitude of the electrical signal applied to the lifter70from the ECU, the deformation of the lifter70may be varied to control the protrusion height H of the inner piston34.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.