CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage entry of PCT Application No: PCT/JP2019/034925 filed Sep. 5, 2019, which claims priority to Japanese Patent Application No. 2018-167882 filed Sep. 7, 2018, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a pump gear, and in particular, to a pump gear configured to be mounted on an input shaft of a supply pump that pumps fuel.

BACKGROUND ART

In a diesel engine equipped with a common rail fuel injection device, fuel in a fuel tank is sent to a supply pump by a feed pump, pressurized to high pressure by the supply pump, and pumped and supplied to a common rail. A pump gear is mounted on an input shaft of the supply pump, and the pump gear is rotationally driven by a crankshaft of the engine via a gear train to drive the supply pump.

CITATION LIST

Patent Literature

PTL 1: Japanese Utility Model Application Laid-Open Publication No. 59-91405

SUMMARY OF INVENTION

Technical Problem

Meanwhile, some pump gears include a hollow portion that is open to a distal end side in an axial direction, and a tapered surface that is formed on an inner peripheral surface of the hollow portion and gradually increases in diameter as it extends from a base end side toward the distal end side in the axial direction. In this case, vibration during driving transmitted from the teeth on an outer peripheral portion of the pump gear is transmitted to the inner peripheral surface of the hollow portion through the flesh of the pump gear and is radiated from the inner peripheral surface of the hollow portion.

At this time, a focusing point of the sound radiation radiated from the inner peripheral surface of the hollow portion is located at the distal end side in the axial direction that is farther than a distal endmost position in the axial direction of the hollow portion, which causes an increased noise when driving the pump gear.

Therefore, the present disclosure was devised in view of such circumstances, and an object of the present disclosure is to provide a pump gear capable of reducing noise during driving of the pump gear.

Solution to Problem

According to one aspect of the present disclosure,

provided is a pump gear configured to be mounted on an input shaft of a supply pump that pumps fuel, which includes

a hollow portion that is open to a distal end side in an axial direction, and

a tapered surface that is formed on an inner peripheral surface of the hollow portion and gradually increases in diameter as it extends from a base end side toward the distal end side in the axial direction,

in which

the tapered surface is configured such that a focusing point of sound radiation radiating perpendicularly from a distal end portion in the axial direction of the tapered surface is positioned at a distal endmost position in the axial direction of the hollow portion or at a position closer to the base end side in the axial direction than the distal endmost position in the axial direction.

Preferably, the pump gear includes

a cylindrical surface formed on the inner peripheral surface of the hollow portion, adjacent to the distal end side of the tapered surface in the axial direction, and formed parallel to the axial direction.

Preferably, the pump gear further includes

a tooth portion formed on an outer peripheral portion of the distal end portion in the axial direction, in which

the distal end portion in the axial direction of the tapered surface is located radially inside in an axial length range of the tooth portion.

Advantageous Effects of Invention

According to the present disclosure, it is possible to reduce noise when driving a pump gear.

