Variable geometry turbocharger

A variable geometry turbocharger (VGT) is provided. The VGT includes a unison ring that rotates a plurality of vanes disposed in a nozzle ring and a sagging prevention mechanism. The sagging prevention mechanism is installed to support the unison ring in a direction opposite to a direction in which a self-weight of the unison ring acts. In particular, the sagging prevention mechanism includes a support pulley that is installed to provide an elastic pressure on an outer circumferential surface of the unison ring in rolling contact therewith.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2019-0092547, filed Jul. 30, 2019, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a structure of a variable geometry turbocharger (VGT) for supercharging with intake air in an engine, and more particularly, to a structure of a VGT that improves stability in controlling vanes therein.

2. Description of the Related Art

The VGT has a plurality of vanes for changing an angle at which exhaust gas in a vehicle engine is supplied to a turbine wheel, and the plurality of vanes are configured to operate by and together with a unison ring. The unison ring is connected to an actuator through a link structure. Once the actuator provides a driving force to rotate the unison ring, the plurality of vanes rotate together, thereby making it possible to adjust a flow rate at which the exhaust gas is incident to the turbine wheel. The unison ring is repeatedly rotated by the actuator as described above, and a plurality of guide rollers are provided inside the unison ring to fix the position of the unison ring and to guide the rotation thereof.

The repeated rotations of the unison ring cause abrasion between the guide rollers and the unison ring as the time for which the VGT has been used elapses. The abrasion phenomenon is affected in a direction in which a self-weight of the unison ring acts, causing the unison ring to sag downwards compared to an initial state. Accordingly, the angles of the vanes when the unison ring sags downwards change from that angles in the initial state, resulting in the reduced accuracy in controlling the VGT.

The contents described as the related art have been provided merely to assist in understanding the background of the present disclosure and should not be considered as corresponding to the related art known to those having ordinary skill in the art.

SUMMARY

An object of the present disclosure is to provide a variable geometry turbocharger (VGT) for suppressing and preventing a change in a position of a unison ring from an initial state according to the position change as the time for which the VGT has been used elapses, thereby improving accuracy and stability in controlling vanes in the VGT.

According to an exemplary embodiment of the present disclosure, a variable geometry turbocharger may include: a unison ring provided to rotate a plurality of vanes disposed in a nozzle ring; and a sagging prevention mechanism installed to support the unison ring in a direction opposite to a direction in which a self-weight of the unison ring acts.

The sagging prevention mechanism may include a support pulley installed to provide an elastic pressure on an outer circumferential surface of the unison ring in rolling contact therewith. Additionally, the sagging prevention mechanism may include: a lower body fixed to the nozzle ring; an upper body installed in a rotatable state relative to the lower body and fixing the support pulley in the rotatable state; and a spring installed to apply an elastic force in a rotational direction between the lower body and the upper body.

The lower body may have an axial projection to provide a rotation axis to the upper body, and the spring may be inserted around an outer surface of the axial projection. The upper body may surround the spring and the axial projection, and may have an arm formed integrally therewith to extend in a direction to fix the support pulley at a position radially spaced apart from the rotation axis for the lower body.

Further, the sagging prevention mechanism may be installed with the support pulley supporting a lower outer circumferential surface of the unison ring. A plurality of sagging prevention mechanisms may be installed at a lower side of the unison ring to be spaced apart from each other. A plurality of guide rollers fixed to the nozzle ring may be disposed inside the unison ring to guide a position and a rotational motion of the unison ring. Each sagging prevention mechanism may be installed between the guide rollers located at the lower side of the unison ring to support the outer circumferential surface of the unison ring.

DETAILED DESCRIPTION

FIG. 1illustrates a partial configuration of a variable geometry turbocharger (VGT). A plurality of vanes3may be rotatably installed in a nozzle ring1fixed to a turbo housing. The rotation axis of each of the vanes3may be connected to a unison ring7through a unison lever5. An actuator9may be connected to the unison ring7via a link11. Accordingly, while the unison ring7is rotated by operation of the actuator9and all of the vanes3are rotated together due to the rotation of the unison ring7, it may be possible to adjust flow of exhaust gas into the turbine wheel, which is located in the center portion of the nozzle ring1but not shown, through openings formed between the nozzle ring1and the vanes3. Notably, the actuator9may be operated by a controller.

Referring toFIGS. 1 to 4, in an exemplary embodiment of the present disclosure, the variable geometry turbocharger may include at least one sagging prevention mechanism13installed to support the unison ring7in a direction opposite to a direction in which a self-weight of the unison ring7acts. The sagging prevention mechanism13may include a support pulley15installed to provide an elastic pressure on an outer circumferential surface of the unison ring7in rolling contact therewith. In other words, the support pulley15may be maintained in rolling contact with the outer circumferential surface of the unison ring7to minimize friction when the unison ring7is rotated, to thus prevent the unison ring7from sagging and ensuring smoother rotation.

In the exemplary embodiment, the sagging prevention mechanism13may include: a lower body17fixed to the nozzle ring1; an upper body19installed in a rotatable state relative to the lower body17and configured to fix the support pulley15in the rotatable state; and a spring21installed to apply an elastic force in a rotational direction between the lower body17and the upper body19. The lower body17may include an axial projection23to provide a rotation axis to the upper body19, and the spring21may be inserted around an outer surface of the axial projection23. The upper body19is structured to surround the spring21and the axial projection23, and may include an arm25formed integrally therewith to extend in a direction to fix the support pulley15at a position radially spaced apart from the rotation axis for the lower body17.

Thus, the elastic force may be applied by the spring21in the rotational direction to the upper body19with respect to the lower body17, and the elastic supporting force may be provided to the outer circumferential surface of the unison ring7through the support pulley15. The lower body17may be configured to be integrally formed in the nozzle ring1. In particular, the axial projection23may protrude integrally from the nozzle ring1.

Furthermore, the sagging prevention mechanism13may be installed with the support pulley15supporting a lower outer circumferential surface of the unison ring7. In other words, since the self-weight of the unison ring7acts downwards, the support pulley15of the sagging prevention mechanism13may be installed at a lower side of the unison ring7to prevent the unison ring7from sagging. In addition, a plurality of sagging prevention mechanism13may be installed at the lower side of the unison ring7to be spaced apart from each other.

In other words, as illustrated inFIG. 2, the sagging prevention mechanisms13may be installed on both sides of the vertical center of the unison ring7to be spaced apart from each other, thereby more stably preventing the unison ring7from sagging. In particular, a plurality of guide rollers27fixed to the nozzle ring1may be disposed inside the unison ring7to guide a position and a rotational motion of the unison ring7. When the sagging prevention mechanism13is installed between the guide rollers27(e.g., each sagging prevention mechanism installed between each guide roller) disposed at the lower side of the unison ring7among all of the guide rollers27to support the outer circumferential surface of the unison ring7, the guide rollers27and the support pulley15may support and guide the unison ring7along a circumferential direction of the unison ring7on an inner circumferential surface and the outer circumferential surface of the unison ring7in an alternating manner, to consistently maintain the position and the rotational motion of the unison ring7in a more stable and smooth state.

Even if abrasion is caused between the guide rollers27located at an upper side and the inner circumferential surface of the unison ring7due to the repeated rotations of the unison ring7, which might result in a situation where the unison ring7sags due to the self-weight thereof, the support pulley15of the sagging prevention mechanism13supports the lower side of the unison ring7to prevent sagging. In addition, even if abrasion is caused between the support pulley15and the unison ring7, the support pulley15may be consistently maintained in close adhesion to the unison ring7by the elastic force of the spring21. Thus, the unison ring7may consistently be maintained in an initially assembled position. When the position of the unison ring7is maintained stably as described above, an angle of each of the vanes3driven by the unison ring7may be controlled more stably and accurately at all times, thereby resulting in a smoother supercharging effect of the VGT and making it possible to secure stable engine output performance.

The present disclosure is capable of stably supporting the position of the unison ring to suppress and prevent a change in the position of the unison ring from an initial state according to the change as the time for which the VGT has been used elapses, thereby improving accuracy and stability in controlling vanes in the VGT.

Although the present disclosure has been shown and described with respect to specific embodiments, it will be apparent to those having ordinary skill in the art that the present disclosure may be variously modified and altered without departing from the spirit and scope of the present disclosure as defined by the following claims.