Yukihito Narita

Mixed and Fluid Film Lubrication Characteristics of Worn Journal Bearings

The mixed and fluid film lubrication characteristics of plain journal bearings with shape changed by wear are numerically examined. A mixed lubrication model that employs both of the asperity-contact mechanism proposed by Greenwood and Williamson and the average flow model proposed by Patir and Cheng includes the effects of adsorbed film and elastic deformation is applied. Considering roughness interaction, the effects of the dent depth and operating conditions on the loci of the journal center, the asperity-contact and hydrodynamic fluid pressures, friction, and leakage are discussed. The following conclusions are drawn. In the mixed lubrication regime, the dent of the bearing noticeably influences the contact and fluid pressures. For smaller dents, the contact pressure and frictional coefficient reduce. In mixed and fluid film lubrication regimes, the pressure and coefficient increase for larger dents. Furthermore, as the dent increases and the Sommerfeld number decreases, the flow rate continuously increases.

Expansion of Ratio Range of Shaft Drive CVT by Using Zero-Spin Disk

The novel mechanism CVT (Shaft Drive CVT, S-CVT) was developed by the authors. It transmits power by a traction drive same as the half toroidal CVT. S-CVT has parallel input/output shafts with conical or concave disks and the idler shaft having conical rollers at both ends, which is placed perpendicularly to the input/output shafts. All disks and rollers can move along each axis directions, and these movements produce the ratio changing by the changes of the rotational radii. The efficiency is the key evaluation function of CVT. To improve the efficiency, the backup roller mechanism was devised. Its effectiveness was confirmed by the experiment, and the efficiency of 95% was obtained by modified prototype S-CVT. This paper deals with the expansion of ratio range of S-CVT. In case of using the present disks, S-CVT has a difficulty to expand the narrow ratio range of 4 (0.5 to 2) because of the large slip brought by the spin. To expand the ratio range, the zero-spin disk/roller was devised. The shape of zero-spin disk/roller satisfies the condition that the spin does not occur at any speed ratio. According to the calculation, the slip rate becomes less than 1% at any speed ratio. To confirm the effectiveness, the prototype S-CVT with zero-spin disk was manufactured. It has the ratio range of 0.43 to 2.35. To obtain the slip rate the experiments were carried out at the speed ratio of 0.43, 1 and 2.35. At each speed ratio, the slip rate of less than 1% was obtained, and the effect of the zerospin disk was confirmed.Copyright

Design of Shaft Drive CVT: Calculation of Transmitted Torque and Efficiency

The novel mechanism of CVT (Shaft Drive CVT, S-CVT) was developed by the authors. To improve the efficiency and the torque capacity of the S-CVT, the theoretical efficiency is calculated in this paper. The efficiency is calculated from the component of torque and the component of velocity. The component of torque is calculated from the loss torque of the bearings. The component of velocity is calculated from the shear model of the traction oil in the EHL contact area. To improve the efficiency and the torque capacity, an optimum design of the two disks/rollers was done by using this calculation. In case of conical disk/roller, 9.4 Nm of the torque capacity and 2.5 point of the efficiency were improved by comparison to the present conical disk/roller. In case of concave disk/roller, though 2.1 point of the efficiency decreased, 58.8 Nm of the torque capacity was improved by comparison with the present.Copyright

Improvement of Efficiency of Shaft Drive CVT by Backup Roller

The authors developed the novel mechanism of CVT, the Shaft Drive CVT. The input shaft and output shaft with conical disks are parallel and an idler shaft having conical rollers at both ends is placed perpendicular to the input/output shafts. This idler shaft transmits torque from the input shaft to the output shaft and its linear motion produces the speed variation by changing the contact point between the input/output disk and the idler roller. To improve the efficiency of the Shaft Drive CVT, the backup conical roller mechanism was devised. It is mounted to the opposite side of the idler roller, and contact with the input/output disk and the backup disk as well as the idler roller. It transmits torque from the input/output disk to the idler roller through the backup disk, and the amount of transmitted torque is enlarged. Moreover, it reduces the bearing loss of the input/output shaft because it supports the axial force of idler roller at the opposite side. The result of theoretical calculation shows the improvement of the power-transmitted efficiency up to 6 points at e = 1. The effectiveness of the backup rollers was confirmed by the experiment, and the efficiency of 98.4% was obtained at e = 2. The magnitude of transmitted torque has increased 1.6 to 1.9 times compared with the case without the backup roller.Copyright

Shaft Drive CVT: A New Type CVT Applying Crossed Axle Traction Drive

The crossed axle traction drive developed by the authors is applied to a new mechanism of CVT, the Shaft Drive CVT. The input and output shafts with conical disks are parallel and a idler shaft having conical rollers at both ends is placed perpendicular to the input/output shafts. This idler shaft transmits a torque from the input shaft to the output shaft and its movement produces the speed variation by changing the contact point between the input/output disks and the idler rollers. The purposes of this study are 1) to propose the new CVT mechanism, 2) to design a curved shape of disk to decrease an amount of spin caused by the movement of contact point, 3) to develop a prototype to confirm the CVT to work and to evaluate the effect of curved disk by means of a power transmission efficiency. The design procedure of shapes of disk and roller are shown by geometrical analysis. The amount of spin is reduced 80% using the proposed concave disk. The range of speed changing ratio of the prototype is 0.5 to 2. The efficiency of 80% was obtained in case of input torque 10 Nm at uniform rate by using the conical disks. The effectiveness of concave disk is evaluated by comparing the experimental results using the conical and concave disks, respectively.Copyright