Trucks, buses, automobiles and industrial equipment are negatively affected by the intrinsic weight, vibrational characteristics and critical speed of metal driveshafts. It has been proven that composite driveshafts are effective in overcoming these limitations. Indeed, the very nature of the composite materials (fiber and resinous binder) allows driveshafts to be designed to meet specific critical operational characteristics, and thus tailored to match the requirements of individual applications. 1.0 SUMMARY AND BACKGROUND Weight, vibrational, fatigue, and critical speed limitations have been recognized as serious problems in automotive and industrial drivetrains for many years. The associated effects and possible solutions have been subjected to detailed analysis. Numerous solutions such as flywheels, harmonic dampers, multiple shafts with additional bearings, and heavy rubber shock (vibration) absorbers have shown limited success in overcoming the problems, but always at the expense of increased weight, rotational inertia, and resistance in the drivetrain. Composite tubing has long been recognized to offer the potential of lighter weight driveshafts. Aerospace development efforts also demonstrated that correctly designed composite components have inherently superior fatigue and vibration damping characteristics to metals. Finally, the advent of higher modulus graphite fibers combined with these lighter weight and vibration damping characteristics allowed the design of driveshafts with much higher critical speed capabilities. These improvements have been realized and the reliability of composite driveshafts has been proven in heavy trucks, on race tracks, in automobiles and light trucks, and in industrial applications. ACPT, Inc. has been designing and producing carbon fiber composite driveshafts for these applications since 1982. 2.0 DRIVETRAIN VIBRATION PROBLEMS Vibration in drivetrains has been recognized as a major problem and has for many years been the subject of much theoretical analysis and trial-and-error vibrational control/reduction experimentation. 2.1 TRUCKS Mazziotti 1 in 1960 published a review and analysis of torsional vibrations associated with drivelines. He delineated some of the sources of non-uniform motion, which result in vibrational excitation of the drivetrain and presented a detailed mathematical analysis relating those sources of excitation to the physical dimensions, mechanical properties, and rotational speeds of driveshafts. He reported data firmly establishing the relationships between non-uniform motion sources and the natural frequency of the driveline components. He concluded that vibrations can be amplified or subdued while being transmitted through the driveline and recommends that (with metal shafts) the driveline be operated at no less than 1.5 times the natural frequency (torsional) of the system. Herein it was assumed that rubber springs, flywheels, flexible couplings and other natural frequency reduction additions were the best way to modify the natural frequency. In 1960 the technology did not exist to design or produce carbon fiber composite driveshafts. Mazziotti also stated that, “a resonant condition can produce objectionable disturbances as follows: 1. The high oscillating torque value can result in failure in rotating members. 2. Variable reactions on supporting members can be a source of objectionable noise and vibration. 3. Damage to gears, bearings, and other components can occur because of non-uniform loading.” All of these predictions have been proven to be accurate and are still sources of aggravation for truck designers, builders and operators. In recognition of, and in order to assist in the design of better truck drive systems, SAE paper #942322, 2 published by Spicer, division of Dana, describes a detailed torsional analysis computer simulation of truck drivetrains. The paper supports Mazziotti’s work and concludes, “torsional vibrations cause comfort problems for occupants and produce component failures.” “Torsionals also introduce dynamic loads on top of the mean static torque transmitted through the power train.” “...could easily cause catastrophic dynamic fatigue failures.” “At least responsible for wear problems at springs, splines, gear teeth, etc, eventually leading to the failure of these components.” This paper also presents a fairly detailed list of references on the subject of vibrations and their effect on automotive drivelines. Higher specific modulus (modulus/density) gives carbon fiber shafts the ability to run longer one piece lengths than metal shafts. A composite shaft, of the same length as a metal shaft, will start to resonate laterally at a much higher speed and have correspondingly increased margin of safety at the higher RPMs. This allows one piece composite shafts to replace two piece steel shafts. The benefits of eliminating the two piece shafts are significant reductions in weight, noise, vibration and harshness. The composite shafts have also proven to dampen vibration and absorb shock, greatly reducing wear on other drivetrain components as well as increasing tire traction. In a test started in August of 1994, a one piece carbon fiber driveshaft was installed in a garbage truck operating in Texas, Figure 2-1 and 2-2. This shaft replaced a two piece steel shaft and a center bearing, Figure 2-3. The resultant weight savings was about 80 lbs. The shaft has now seen daily use for the last two years in what has been described as one of the most torturous commercial truck applications possible. Absolutely no problems have been recorded. The operator is maintaining records of repairs with which to compare histories with other driveline components of identical trucks in the fleet. It is still too early to draw any conclusions from these records. It can be said, however, that the carbon fiber shaft is performing flawlessly. Figure 2-1: Garbage Truck Operating with One Piece Carbon Fiber Driveshaft The garbage truck shaft replacement was a cooperative effort with Inland Empire Driveline Services, Ontario, CA. They have been instrumental in helping us to develop and supply carbon fiber driveshafts to the automotive community. Inland has successfully developed and employs aluminum welding techniques, which resulted in moving torque testing failures from the weld joint to the U-joint. They have provided constant support in obtaining information and hardware mating carbon fiber tubing to the correct driveshaft fittings. Inland Empire Driveline Services continues to be of great technical assistance and currently performs all of the welding and balancing required in the manufacture of our carbon fiber driveshafts. Other direct experience is being obtained from OEM’s. Three major OEMs have run composite driveshafts on test tracks and have performed extensive laboratory evaluations. One of these companies is now running “on the road” fleet evaluations. 2.2 AUTOMOTIVE AND LIGHT TRUCKS The vibration problems in automobiles and light trucks are not so much “catastrophic failures”, but rather more of weight, noise, harshness and passenger discomfort. Component failure can still be a problem at high speeds, as natural resonant frequencies of the driveshaft are approached. GKN 3 states that, “the Mark VIII is top speed limited by its long steel driveshaft to 128 mph. Above 128 mph the driveshaft gets into a bending and vibration frequency that would eventually tear it apart.” They continue that, “to eliminate this problem most high speed European cars usually have a two piece shaft connected through a center bearing.” Carbon fiber driveshafts can alleviate this problem. 2.3 INDUSTRY Heavy duty industrial drivetrains, such as pump shafts and cooling tower driveshafts, suffer from similar torsional vibrations, natural frequency, and critical speed problems as heavy duty trucks and buses. The industrial community has demonstrated that composite driveshafts will reliably solve these problems. Figure 2-2: One Piece Carbon Fiber Driveshaft, Garbage