Worm Gearbox Research Articles

Tribological Study of Grease Lubricated Plastic Wormgear for Automotive Applications

Plastic wormgear has many application opportunities in automotive industry because of its low noise and lightweight properties. Three major concerns about plastic wormgear are bending strength, efficiency or friction, and wear. Since standard worm and wormgear designs are developed mainly for metal gears, they are not applicable for the design of plastic wormgear. This paper presented a non-standard design to increase the bending strength of plastic wormgear. By increasing gear contact ratio, the maximum contact stress on the plastic gear tooth was reduced to prevent wear of the plastic wormgear flank. The load, speed, and grease effects on gearbox efficiency and friction coefficient were experimentally studied. While load had a major effect on friction coefficient of grease lubricated plastic wormgear, the speed had much less influence on the friction coefficient of the plastic wormgear. Misalignment of the worm shaft had significant impact on the efficiency of the worm gearbox. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2001

The Thermal Rating of Worm Gearboxes

The paper deals with the factors affecting the temperature rise of totally enclosed self-lubricated gearboxes, with particular reference to worm gearboxes, and is based on observations obtained from a power circulating apparatus through worm gears which has provision for the accurate measurement of efficiency and temperature rise under variable load and speed. The theory underlying the heating and cooling of gearboxes is discussed, for gears running under continuous load and also under a repeated cycle of intermittent load. Temperature rise depends on the heat-dissipating capacity of the gearbox and the power losses within the box; heat-dissipating capacity is dealt with in relation to surface area of the box, speed of the gears, and artificial cooling by air fan; power losses are discussed under the headings of efficiency and oil drag losses. It is shown that gear speed and turbulence in the lubricant contribute considerably to heat-dissipating capacity, and that oil drag losses play an important part, particularly on large gears running at moderate or high speed. Cooling by air or other means is shown to result in an increase in power capacity (for a given allowable temperature rise) much more than in proportion to the increase in heat-dissipating capacity of the box, owing to a higher overall efficiency when transmitting heavier loads. Results of worm gear efficiency tests carried out in the past on the Daimler-Lanchester testing machine at the National Physical Laboratory on the author's design of worm gear, which gave the highest efficiency of any published tests carried out on this machine, are reconsidered in the light of recent work and it is contended that the National Physical Laboratory machine gives efficiency figures which are in general higher than the true efficiency.