ypical Globoid gear.
Globoid (or Double Enveloping Worm or Hour Glass) gear has advantage pitched against a traditional worm equipment due to increased driving efficiency ( 6-10% higher on 25:1 ratio) and increased loading capacity (about 30%).
The disadvantage of a globoid gear is higher manufacturing cost and sensitivity of the enveloping pinion to the axial location.
Due to the geometrical nature of the tooth geometry Globoid pinion may mesh not only with the mating enveloping gear but also with a properly designed cylindrical helical gear. Using a helical gear with a Globoid pinion is definitely common in reduced cost in applications such as automotive electric powered gear actuators. The significant price advantage comes due to the likelihood to injection mold the helical plastic material gear. The load capacity of the simplified helical/Globoid transmission is decreased to the level below the load capacity of the regular worm gear. Nevertheless the driving efficiency is still better compare to the regular worm gear.
There are just a few suppliers of the Globoid gear. division of Textron, situated in Traverse Town, MI. The detailed information regarding procedures utilized at Cone Drive for developing of its gear cannot be found. However, based on publicly released info it can be understood that the gear is manufactured by CNC milling with use a small ball shaped cutter.
globoid worm Ever-power has capacity to design, prototype and offer Globoid gear items. The knowledge of Ever-power is 3-dimentional simulation and modeling of the Globoid and dual enveloping tooth geometry. Ever-power 3-dimentional Globoid and double enveloping gear CAD models can be used in numerous CNC machining shops for making globoid gear at considerably reduced cost.
Ever-power Globoid 3-dimentional CAD model.
It needs to be noted that manufacturing of the Globoid gear is more technical compare to production of the Globoid pinion. The Globoid pinion could be produced in high amounts by turning, whirling or grinding. During the machining process of the Globoid pinion the cutting tool needs to be able to tilt to be able to produce the enveloping form.
The newer production methods are under advancement. The most promising production method of the Globoid pinion is usually continues grinding procedure, which incorporates a grinding wheel (diamond or CBN plated) with particular Ever-power simulated geometry. The complication of the novel procedure is the difficulties with simulation of the geometry of the grinding device. The grinding tooth would have to generate a correct form of the Globoid pinion without tilting therefore the production price and the production cost would be considerably reduced. Ever-power is rolling out a computer based tool for creating of 3-dimensional CAD types of grinding equipment for high volume creation of the Globoid products.
The most common use of the Globoid gear set was seen in 1961-1989 on automotive steering systems in Italy and in Soviet Union.
VAZ-2101 with Globoid steering technology.
The Globoid pinions have been produced by grinding with a tilting grinding wheel. The Globoid gears have already been cut by a special hub, which replicated the form of the Globoid Pinion. Special machines for generating the trimming hubs have already been developed. As the modern motor vehicle steering systems started to use traditional Bishop or advanced Ever-power adjustable ratio rack and pinion technology, the demand for the Globoid gears has been reduced.
Variable ratio technology comparison
Bishop
Ever-power
Vr-rack technology was introduced:
Before 2000
2000
Underlying mathematical model is founded on:
Classic
gear
theory
Direct
Digital
Simulation
Rack geometry calculation accuracy is:
Limited by the boundaries of the classic gear theory
Unlimited
Capability to produce the vr-rack with not involute form for reduced noise
NO
YES
Capacity to generate vr-rack with increased ratio gain is:
Limited
YES
Cost of vr-rack design is:
High
Low
Ever-power advanced Variable Ratio rack and pinion high ratio gain technology for engine sport racing applications.
Ever-power low noise Variable Ratio rack and pinion not involute technology.
Ever-power pioneered in developing of another generation of Globoid gears. In 1999 Ever-power released a skew axis Globoid gear as a high load capacity and increased driving efficiency alternative to the classic Globoid equipment.
Ever-power skew axis (wormoid) gear.
It needs to be noted that the name WORMOID will not relate with any scientific term in fact it is something of Dr. Stepan V. Lunin, who was the 1st in proposing this design and, more importantly, he was the 1st who produces a precise functioning model of the apparatus in 3-dimantional CAD system. The accurate 3-d CAD of the WORMOID equipment has proved the capability of the idea such as conjugated transmission action and significant boost of number of tooth in the contact compare to the traditional Globoid gear.
CAD 3-d style of Ever-power wormoid gear.
Ever-power is currently offering assistance for design and development of items predicated on Ever-power wormoid technology.
It needs to be noted that wormoid gear style from Ever-power is obviously promising unique advantages compare to the common Globoid (double enveloping) equipment. Among the obvious advantages is improved load capacity because of increased number of the teeth in the mesh. The apparatus torque is normally carried by even more teeth so the load on each individual tooth is reduced. The other apparent advantage is increase driving efficiency. As one can see, the portion of the pinion with larger diameter is generating the corresponding part of the gear, which has a larger diameter as well. Such of unique feature of Ever-power wormoid is certainly missing in the traditional Globoid gear and results in higher sliding velocities and higher friction drug on the traditional globoid gear. An experienced in the art engineer would instantly derive possible design advantages of the wormoid equipment. For example, using of the wormoid gear can significantly reduce cost of electric powered assist mechanisms that are generally applied to modern automobiles. Due to the bigger driving efficiency, wormoid equipment set can be made with increase ration and provide the same driving efficiency as the original worm or double enveloping worm equipment. For instance NSK worm equipment steering actuator with a ration of about 20:1 delivers about 80% of driving efficiency. The plastic gear would hold about 80 Hm of torque. An alternative wormoid gear design from Ever-power would be capable to increase the ratio up to 30:1 and the torque on the apparatus up to 150 Hm without increase of the guts distance between the equipment and the pinion.