Gards Inc/s New Gearless Drive: Low Noise With Gear-Like Flexibility
Gards, Inc., of Bellevue, Wash, has introduced a new gearless hydraulic marine propulsion system it says reduces noise and load but gives operators the flexibility of a geared system: continuous stepless speed control, instant full power reversal, power steering and simple transfer from main propulsion to side thrusting. Gards says its interactive twin-rotor hydraulic motor overcomes the inefficiencies that hindered wide application of hydraulic propulsion, and was designed specifically for marine application where long hours of continuous operation under heavy conditions is common.
The propeller drive units consist of two interactive rotors connected by angular pistons which are pressurized simultaneously in both rotors, developing the "wedge effect" which then drives the rotors. Very high overall efficiency is reportedly achieved with this patented design. Gards says the few moving parts carrying the load under optimum distribution assure high operating reliability, low maintenance requirements and long life. Since all the moving components of the hydraulic pump and propeller drive unit are enclosed and submerged in hydraulic fluids, no additional lubrication is necessary - virtually eliminating mechanical failures due to corrosion or lack of lubrication. The propeller drive unit can be mounted steerable so the steering of the vessel becomes easier at any speed, even at standstill or during docking. Drive units from 50 to 400 hp are being developed.
Noise reduction is achieved in several ways: the engine can be positioned for optimum noise reduction, because the engine and the propeller shaft are connected by flexible hoses instead of a drive shaft; anti-vibration engine mounting; axial water inflow to the propeller can be achieved, reducing vibrational levels of inclined shafts; and increased separation of the propeller from the hull. The final drive unit, having high torque output, can be operated at medium pressure without the need for a high-pressure hydraulic pump in combination with a gear drive, which are also sources of high-level noise. The elimination of the drive shaft and gear drives also means the engine can be positioned for optimum load distribution and balance, and overall weight is reduced.
The combination of a variable displacement hydraulic pump and a fixed displacement high torque hydraulic motor serves as an optimum speed/torque converter.
Energy in the form of pressurized fluids is transferred from the pump to the propeller drive, where it is converted back into mechanical energy. The replacement of the mechanical transmission by hydraulic components provides stepless speed control from standstill to full speed, as well as instant reversal, reportedly assuring the availability of full power at any moment.
The high-efficiency hydraulic drive allows the distribution of power from a single power source to multiple propeller drives.
Having no mechanical connections between the engine-pump unit and the propeller drive units, the marine architect has complete freedom in positioning single or multiple propeller drives both on the bow and stern sections.
For more information on Gards Inc.'s new gearless hydraulic drive