Valve spring device and valve train of internal combustion engine using the same

A valve train of an engine, comprising:

• a valve including a valve disc for opening and closing a port formed in a cylinder head;
• a drive mechanism which drives the valve in an opening direction by means of a rotating cam;
• and
• a valve spring device which drives the valve in a closing direction, the valve spring device including:
• a first spring, formed of a compression coil spring and deformable in an axial direction of the valve, and
• a second spring disposed in series with the first spring and held by a stopper in a manner such that the second spring is subjected to a preload by axial compression,
• wherein the preload of the second spring is larger than an installation load of the first spring, and wherein the valve spring device has load-deflection characteristics such that only the first spring deforms axially when an axial load which acts in a direction to compress the first spring is not larger than a predetermined value, and such that the first and second springs deform axially when the axial load exceeds the predetermined value,
• wherein the drive mechanism has a function to deform only the first spring axially and a function to deform both the first and second springs axially, and
• wherein the cam of the drive mechanism has a first cam surface which deforms only the first spring axially, thereby bringing at least some turns of a wire of the first spring into contact with one another, and a second cam surface which deforms the second spring axially with at least some turns of the wire of the first spring kept in contact with one another.