Proceedings ofDR WTC2005AFT World Tribology Congress III September 12-16, 2005, Washington, D.C., USA Proceedings of WTC2005: World Tribology Congress III September 12-16, 2005, Washington,D.C., U.S.A. WTC2005-63073

WTC2005-63073

DEVELOPMENT OF FRICTION DRIVE

Xiaolan Ai, Matthew Wilmer and David Lawrentz The Timken Company

ABSTRACT friction drive were fabricated for testing. Major geometry parameters are listed in Table 1. Friction drive is a mechanical device that utilizes friction force to transmit and power. Since the power is Table 1 Geometric parameters of friction drive prototype transferred through shearing a thin layer of highly pressurized lubricant film formed between the mating surfaces. Friction Component Parameter Value (mm) drive possesses desired performance attributes that pertain to its Outer ring and shaft raceway diameter 100 unique operating principles. These attributes include high effective raceway 11 mechanical efficiency, minimal backlash, low noise and width vibration and high-speed capability. The power density of a section thickness 10 friction drive can be very high when operated at elevated web thickness 1.5 speeds. These performance features, in conjunction with its Sun roller raceway diameter 20 inherent manufacturing simplicity, make friction drives suitable effective raceway 11 candidates for a host of applications. The current global width technology trend towards electrification and increasing use of Loading planet raceway diameter 50 electric machines in auxiliary drives for both automotive and raceway width 11 industrial applications presents a good opportunity for friction section thickness 7.5 drives as a cost-effective alternative to conventional gear eccentricity 10 drives. The smooth high-speed performance feature of friction drives allows the use of more efficient high-speed motors to Extensive testing was conducted to evaluate its reduce motor size and thus improve system power density performance. Figure 2 shows the schematic of test apparatus. It A novel cylindrical friction drive was developed [1,2] for is comprised of a drive motor, a high-speed spindle, and a electric oil pump applications. The friction drive is to be pump. The motor drives the spindle through a integrated with an to provide necessary speed rubber and a pair of pulleys. The spindle shaft connects to reduction. The friction drive, as shown in Figure 1, is the input shaft of the friction drive thought an input torque comprised of an outer ring, a sun roller, a loading planet, two meter. The output shaft of the friction drive couples to the supporting planets and a stationary carrier. The sun roller is set hydraulic pump through an output torque meter. The torque eccentric to the outer ring to generate a wedge gap that meters pick up both speed and torque signals at input and facilitates a torque actuated loading mechanism for the friction output shafts of the friction drive, respectively. Thermo-couples drive. The loading planet is properly assembled in the wedge are mounted to monitor temperatures at planet support shafts gap with frictional contact with the sun roller and the outer ring and at bearings of input and output shafts. An accelerometer and is elastically supported on the carrier. By altering the ratio was placed on the back plate of a mounting bracket to which of the support stiffness to contact stiffness, the actual operating the friction drive was bolted. It monitors the vibration signals of friction coefficient of the friction drive can be changed to suit the friction drive for reference and safety purposes. A data for desired performance regardless the wedge angle. This acquisition system was used to collect and process all signals at provides a grater freedom for design optimization predetermined sampling rate. Design analysis was presented and a FE model was The friction drive offered a consistent smooth and quite developed to quantify design parameters. Prototypes of the performance over a wide range of operating conditions. It was

1 1 CopyrightCopy ©ri 2005ght © by # ASME### by ASME capable of operating at an elevated speed of up to 12000 rpm with adequate thermal characteristics. Figure 3 shows the REFERENCES steady sate temperature contour map as function of input shaft speed and output shaft torque. 1. Ai, X., 2004, “Wedge Loading Mechanism for Results demonstrated that the friction drive has high power Traction Drives,” Patent Cooperation Treaty (PCT), transmission efficiency under various test conditions. The peak International Publication No. WO 2004/029480 A1 efficiency exceeded 97%. Figure 4 plots the overall system 2. Ai, X., 2003, “Eccentric Planetary Drive efficiency as a function of output torque for various input Transmission,” Patent Cooperation Treaty (PCT), speeds. Results also confirmed that the stiffness of the elastic International Publication No. WO 03/06489 A1 support has an important impact on performance. The elastic support stiffness, in conjunction with, the contact stiffness determines the actual operating friction coefficient at the frictional contacts

Figure 3 Thermal Characteristic of the Friction Drive

1.1 Figure 1 Friction Drive Assembly 1.05 1 Torque Meter Torque Meter High Speed 0.95 Spindle (output) Friction Drive (input) 0.9 Input Speed 0.85 2000 rpm cy 3000 rpm 0.8 en 4000 rpm ci i f

f 0.75 5000 rpm

Hydraulic E 6000 rpm Brake Pump 0.7 7000 rpm 8000 rpm 0.65 9000 rpm Electric Motor 0.6 10000 rpm 0.1 11000 rpm 12000 rpm 0.05

0 5000 10000 20000 25000 35000 40000 0 15000 30000 45000 Output Torque (Nmm)

Figure 4 Dynamic Efficiency of Friction Drive under Various Conditions

Figure 2 Schematic of Mechanical Layout of Test Apparatus

2 2 CopyrightCopy ©ri 2005ght © by # ASME### by ASME