Composite gear housing
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Fiber reinforced composite material is used for weight reduction of engineering structures. Carbon fiber reinforced composite plastic material is commonly used in the aerospace industry. John Barnard tried to incorporate this material in a gear housing for Ferrari in 1994, but instead only mounted the metal gear case on a carbon fiber composite support. In 1998, Barnard (then at Arrows) and Alan Jenkins (at Stewart F1) both incorporated carbon fiber composite gear cases. Since then both Honda (nee B.A.R) and McLaren have raced Carbon cases since 2003. The advantage of reduced weight of the gear transmission housing is greater possible acceleration.
In 1969 General Motors investigated using composite transmission case to reduce manufacturing cost.
In 2004 the US Department of Defense decided to finance development of a composite gear housing for a main rotor helicopter planetary gear box. Boeing and Sikorsky currently conduct the development of helicopter composite gear housing.
The main problem of using fiber reinforced composite plastic for gear housing is low thermal conductivity and low hardness of the composite material. Because of the low hardness, the composite gear housing would necessarily have numerous metal inserts laminated into the composite exterior or installed with adhesive in the prefabricated composite housing. High strength epoxy adhesives are used in fabrication of carbon fiber composite drive shafts for cars.
The metal inserts are typically round shaped and provide support for bearings, shafts, gears and other metal components of the gearbox. Low thermal conductivity prevents transmission of heat through the composite gear housing. The composite gear housing does not remove heat as efficiently as an aluminum or magnesium housing. Composite gear housings require more expensive and reliable cooling systems. However, composite plastic material is widely used on low-power applications such as gear motors for electromechanical actuators. Lightly loaded rotary gear actuators can be completely made of composite plastic material. Such electromechanical rotary actuators are installed, for example, on power windows of automobiles. Higher loaded actuators can contain metallic gears inside plastic composite housing for reduction of cost and corrosion resistance.
Some modern industrial robots incorporate electromechanical rotary gear actuators installed inside carbon fiber composite housing – robotic arm. Using carbon fiber material for robotic arm allows to reduce inertia of the arm and as a result makes robot operate faster. http://gearmechanic.com Gear Mechanic Corporation in Las Vegas, NV manufacturing composite gear housings for automotive and aerospace applications along with worm face gears. Gear Mechanic Co. uses composite gear housing for making a light weight and low inertia hypoid gear case for a racing car drive axles. Lower inertia allows faster acceleration and faster stopping which results in significant advantage on NASCAR racing and FORMULA ONE racing. In a modern airplane one can find numerous mechanical systems with gears, power drive units, drive shafts, actuators, hoists and other mechanical parts. People used to call helicopters "flying transmissions". Today an average airplane has more transmission components than a helicopter. The common transmission mechanical components of an airplane are: high lift system, bay door actuation system, cargo door actuation system, landing gears, hoists, cargo door actuation systems and sometimes primary flight control system. The overall cost and weight of the mechanical system of an airplane can be similar to the cost and weight of the helicopter transmission. Reduction of weight and cost of mechanical systems is important for reduction of the overall operating cost of the airplane.
While the generic idea of a composite gear can be traced back to 1924 (US patent # 1485464) the first aerospace adoption on electromechanical rotary actuators was patented by Curtiss-Wright Controls in 1994 (US patents # 5518466, 5779587, 6705570). Curtiss-Wright patents describe a concept of a fail-safe aerospace electromechanical rotary actuator for flight controls and for other use. The key element of Curtiss-Wright invention is a ring gear. By Curtis-Wright invention the actuator ring gear is not a single part but it is a composition of a few simple elements making the ring gear composite. Curtiss-Wright composite ring gear invention allows not only the cost reduction of the rotary actuator by providing an opportunity to use different materials for the gear and for the housing, but it also allows to use Curtiss-Wright composite ring gears for primary flight controls because of fail safe feature. The concept of Curtiss-Wright composite gear is simple: when the load exceeds the limit the ring gear spins inside the housing. With development of new adhesives and fiber reinforced plastic materials Curtiss-Wright invention gets a fresh kick. By Curtiss-Wright invention, the housing of the ring gear is made separately from the ring gear, so different materials can be used for manufacturing the ring gear and for the housing. Today, fiber reinforced composite plastic materials are most used materials in aerospace. Because of more stable fatigue properties of fiber reinforced plastics the fail tolerant feature of Curtis-Wright invention can provide more accurate performance.
Gear Mechanic Co. has developed controlled bonding methods and mathematical simulation methods for three dimensional filament wound composite structures used in mechanical systems. The method provides optimized fiber placement and increased strength of bonding between metal inserts and fiber reinforced plasticsfor metal/composite power transmission components in different applications.
