1. Field of the Invention
The invention relates to a frictional hinge device which is used to pivotably support a lid and display of a portable business such as a laptop note type personal computer, and particularly concerns to a frictional hinge device used to frictionally hold the lid and display at desired pivotal angles.
2. Description of Prior Art
This type of the frictional hinge device is disclosed by Laid-open Japanese Patent Application No. 5-154864. This teaches that an outer shaft is made of a synthetic resin and integrally molded with an inner shaft. Due to a surface frictional resistance between the inner and outer shafts, it is possible to frictionally hold the inner shaft at the desired pivotal angle while permitting the inner shaft to rotate relative to the outer shaft against the force of the surface frictional resistance therebetween.
However, the disclosure remains silent about qualitative and quantitative analyses on the relationship between the inner and outer shafts. This causes no smaller variations on torque when the inner shaft pivotally moves. This also causes abnormal noise due to a stickslip phenomenon when pivotally moving the inner shaft while losing a good endurance with a torque reduced due to an unacceptable amount of wear between the inner and outer shafts.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide a frictional hinge device which is capable of maintaining a stable frictional resistance between a shaft member and a support member for an extended period of time when frictionally holding the shaft member at desired pivotal angles based on the frictional surface resistance.
With a support member made of a resin molded to surround a shaft member, the support member tightly engages with the shaft member due to a residual stress established by a shrinkage allowance after molding the support member in integral with the shaft member. During the molding process, the synthetic resin is injected into a die mold in which the shaft member was beforehand placed.
When a surface frictional resistance appeared between the support member and the shaft member is smaller than an exterior torque to which the shaft member is subjected, the shaft member pivotally moves relative to the support member. When the surface frictional resistance exceeds the exterior torque, the shaft member is held at a desired pivotal angle due to the surface frictional resistance.
With the support member and the shaft member molded integrally, it is possible to manufacture them less costly while making it possible to readily determine the surface frictional resistance necessary to frictionally hold the shaft member at the desired pivotal position because the shaft member is provided with a surface roughness ranging 0.15 to 0.35 xcexcm. This avoids an abnormal noise caused from the stickslip phenomenon, and exceedingly reduces the wear dust produced between the support member and the shaft member to maintain a stable surface frictional resistance therebetween for an extended period of time.
With the frictional hinge device used to pivotably move a display for a portable business device, it is possible to hold the display at desired angles to ensure a good position for visually recognizing what the display shows.