US-20260126103-A1 - POWER TRANSMISSION DEVICE

US20260126103A1US 20260126103 A1US20260126103 A1US 20260126103A1US-20260126103-A1

Abstract

A planetary gear mechanism may include a sun gear fixed to a shaft, a ring gear located coaxially with the sun gear and fixed to a case, a planetary gear meshed with the sun gear and the ring gear, and a carrier configured to rotatably support the planetary gear. A helix angle of teeth of the sun gear and a helix angle of teeth of the ring gear may be set so that a thrust force acting on the sun gear and a thrust force acting on the ring gear are in opposite directions. A power transmission device may include a load transmission path between the sun gear and the ring gear, through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path may include at least a portion of the carrier.

Inventors

Yoshito SEKIGUCHI

Assignees

TOYOTA JIDOSHA KABUSHIKI KAISHA

Dates

Publication Date: 20260507
Application Date: 20251105
Priority Date: 20241107

Claims (7)

1 . A power transmission device comprising a planetary gear mechanism and a case housing the planetary gear mechanism, wherein the planetary gear mechanism comprises: a sun gear fixed to a shaft configured to rotate; a ring gear located coaxially with the sun gear and fixed to the case; a planetary gear meshed with the sun gear and the ring gear; and a carrier configured to rotatably support the planetary gear, the carrier being located coaxially with the sun gear and supported rotatably with respect to the case, wherein the sun gear and the ring gear are each a helical gear, a helix angle of teeth of the sun gear and a helix angle of teeth of the ring gear are set so that a thrust force acting on the sun gear and a thrust force acting on the ring gear are in opposite directions, the power transmission device further comprises a load transmission path between the sun gear and the ring gear, through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path includes at least a portion of the carrier.
2 . The power transmission device according to claim 1 , wherein the load transmission path includes a first bearing interposed on a path between the sun gear and the carrier and a second bearing interposed on a path between the ring gear and the carrier.
3 . The power transmission device according to claim 2 , wherein the carrier is connected to a differential case housing a differential gear, and the first bearing is sandwiched between the sun gear and the differential case.
4 . The power transmission device according to claim 2 , wherein the load transmission path includes a structure extending from the ring gear, and the second bearing is sandwiched between the structure and the carrier.
5 . The power transmission device according to claim 4 , wherein the structure is integrally molded with the ring gear.
6 . The power transmission device according to claim 1 , wherein the planetary gear is a stepped pinion having a large-diameter pinion meshed with the sun gear on one side in an axial direction parallel to the shaft and a small-diameter pinion meshed with the ring gear on another side in the axial direction, and the load transmission path is provided on the other side of the large-diameter pinion in the axial direction.
7 . The power transmission device according to claim 1 , the helix angle of the teeth of the sun gear and the helix angle of the teeth of the ring gear are set so that a magnitude of the thrust force acting on the sun gear and a magnitude of the thrust force acting on the ring gear are equal to each other.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority from Japanese Patent Application No. 2024-195119 filed on November 7, 2024. The entire content of the priority application is incorporated herein by reference. TECHNICAL FIELD The art disclosed herein relates to a power transmission device comprising a planetary gear mechanism and a case housing the planetary gear mechanism. BACKGROUND ART As one of power transmission devices, Japanese Patent Application Publication No. 2021-110374 describes a transaxle configured to transmit power of an electric machine to an axle via a planetary gear reduction drive and a differential device. According to Japanese Patent Application Publication No. 2021-110374, the planetary gear reduction drive uses a sun gear arranged on an output shaft of the electric machine as an input element, a ring gear fixed to a case housing the planetary gear reduction drive as a reaction element, and a carrier as an output element. The carrier supports stepped pinions each of which includes a large-diameter pinion meshed with the sun gear and a small-diameter pinion meshed with the ring gear so that the stepped pinion rotates about its axis and revolves around the sun gear. Japanese Patent Application Publication No. 2021-110374 describes that each gear constituting the planetary gear reduction drive is a helical gear. SUMMARY In the above-mentioned planetary gear mechanism, since the ring gear is a helical gear, the ring gear is subjected to a thrust force. The thrust force to which the ring gear is subjected would be received by the case to which the ring gear is fixed. Accordingly, rigidity of the case needs to be ensured in order to receive the thrust force acting on the ring gear, which resulted in problems that a thickness and/or size of the case are increased. A power transmission device may comprise a planetary gear mechanism and a case housing the planetary gear mechanism, wherein the planetary gear mechanism may comprise: a sun gear fixed to a shaft configured to rotate; a ring gear located coaxially with the sun gear and fixed to the case; a planetary gear meshed with the sun gear and the ring gear; and a carrier configured to rotatably support the planetary gear, the carrier being located coaxially with the sun gear and supported rotatably with respect to the case. The sun gear and the ring gear may be each a helical gear, a helix angle of teeth of the sun gear and a helix angle of teeth of the ring gear are set so that a thrust force acting on the sun gear and a thrust force acting on the ring gear are in opposite directions. The power transmission device may further comprise a load transmission path between the sun gear and the ring gear, through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path may include at least a portion of the carrier. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 illustrates a simplified diagram of a configuration of a power transmission device. FIG. 2 illustrates a simplified perspective view of an outer appearance of a case and contents within the case. FIG. 3 illustrates a partial cross-sectional view primarily showing a planetary gear mechanism within the case. FIG. 4 illustrates a simplified side view of a vehicle in which the power transmission device is mounted. DETAILED DESCRIPTION In one aspect of the present teachings, a power transmission device may comprise a planetary gear mechanism and a case housing the planetary gear mechanism, wherein the planetary gear mechanism may comprise: a sun gear fixed to a shaft configured to rotate; a ring gear located coaxially with the sun gear and fixed to the case; a planetary gear meshed with the sun gear and the ring gear; and a carrier configured to rotatably support the planetary gear, the carrier being located coaxially with the sun gear and supported rotatably with respect to the case. The sun gear and the ring gear may be each a helical gear, a helix angle of teeth of the sun gear and a helix angle of teeth of the ring gear are set so that a thrust force acting on the sun gear and a thrust force acting on the ring gear are in opposite directions. The power transmission device may further comprise a load transmission path between the sun gear and the ring gear, through which the thrust force acting on the sun gear and the thrust force acting on the ring gear are transmitted, and the load transmission path may include at least a portion of the carrier. According to this configuration, the thrust force acting on the ring gear and the thrust force acting on the sun gear and oriented opposite from the thrust force acting on the ring gear are both transmitted to the load transmission path. Accordingly, at least a portion of the thrust force acting on the ring gear is cancelled by the thrust force acting on the sun gear. Due to this, the rigidity required for the case to have to receive the trust force acting