Globoid Gear technology from ZAKGEAR.

By Dr. Stepan V. Lunin.

2007.

Picture 1. Typical Globoid gear.

Globoid (or Double Enveloping Worm or Hour Glass) gear has advantage versus a traditional worm gear because of 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 can mesh not only with the mating enveloping gear but also with a correctly designed cylindrical helical gear. Using a helical gear with a Globoid pinion is common in reduced cost in applications such as automotive electric powered gear actuators. The significant cost advantage comes due to the possibility to injection mold the helical plastic gear. The load capacity of the simplified helical/Globoid transmission is reduced to the level below the load capacity of the regular worm gear. However the driving efficiency is still better compare to the regular worm gear.

There are just a few suppliers of the Globoid gear. The most known US supplier of the gears similar to Globoid gear is Cone Drive, division of Textron, located in Traverse City, MI. The detailed information about processes used at Cone Drive for manufacturing of its gear could not be found. However, based on publicly released information it can be understood that the gear is manufactured by CNC milling with use a small ball shaped cutter.

ZAKGEAR has capability to design, prototype and supply Globoid gear products. The expertise of ZAKGEAR is 3-dimentional simulation and modeling of the Globoid and double enveloping tooth geometry. ZAKGEAR 3-dimentional Globoid and double enveloping gear CAD models can be used in numerous CNC machining shops for producing globoid gear at significantly reduced cost.

Picture 2. ZAKGEAR Globoid 3-dimentional CAD model.

It has to be noted that manufacturing of the Globoid gear is more complex compare to manufacturing of the Globoid pinion. The Globoid pinion can be produced in high quantities by turning, whirling or grinding. During the machining process of the Globoid pinion the cutting tool has to be capable to tilt in order to produce the enveloping shape.

The newer production methods are under development. The most promising production method of the Globoid pinion is continues grinding process, which incorporates a grinding wheel (diamond or CBN plated) with specific ZAKGEAR simulated geometry. The complication of the novel process is the difficulties with simulation of the geometry of the grinding tool. The grinding tooth would have to generate a correct form of the Globoid pinion without tilting so the production rate and the production cost would be significantly reduced. ZAKGEAR has developed a computer based tool for producing of 3-dimensional CAD models of grinding tools for high volume production of the Globoid products.

The most common use of the Globoid gear set was noticed in 1961-1989 on automotive steering systems in Italy and in Soviet Union.

Picture 3. VAZ-2101 with Globoid steering technology.

The Globoid pinions have been produced by grinding with a tilting grinding wheel. The Globoid gears have been cut by a special hub, which replicated the shape of the Globoid Pinion. Special machines for producing the cutting hubs have been developed. Because the modern automotive steering systems started to use classic Bishop or advanced ZAKGEAR variable ratio rack and pinion technology, the demand for the Globoid gears has been reduced.

Variable ratio technology comparison

Bishop

ZAKGEAR

Vr-rack technology was introduced:

Before 2000

2000

Underlying mathematical model is based 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

Capability to generate vr-rack with increased ratio gain is:

Limited

YES

Cost of vr-rack design is:

High

Low

Picture 4. ZAKGEAR advanced Variable Ratio rack and pinion high ratio gain technology for motor sport racing applications.

Picture 5. ZAKGEAR low noise Variable Ratio rack and pinion not involute technology.

ZAKGEAR pioneered in developing of the next generation of Globoid gears. In 1999 ZAKGEAR introduced a skew axis Globoid gear as a high load capacity and increased driving efficiency alternative to the classic Globoid gear.

Picture 6. ZAKGEAR skew axis (wormoid) gear.

It has to be noted that the name WORMOID does not relate to any scientific term and it is a product of Dr. Stepan V. Lunin, who was the first in proposing this design and, more importantly, he was the first who produces an accurate working model of the gear in 3-dimantional CAD system. The accurate 3-d CAD of the WORMOID gear has proved the capability of the concept such as conjugated transmission action and significant increase of number of teeth in the contact compare to the classic Globoid gear.

Picture 7. CAD 3-d model of ZAKGEAR wormoid gear.

 

ZAKGEAR is currently offering assistance for design and development of products based on ZAKGEAR wormoid technology.

It has to be noted that wormoid gear design from ZAKGEAR is obviously promising unique advantages compare to the classic Globoid (double enveloping) gear. One of the obvious advantages is increased load capacity due to increased number of the teeth in the mesh. The gear torque is carried by more teeth so the load on each individual tooth is reduced. The other obvious advantage is increase driving efficiency. As one can see, the portion of the pinion with larger diameter is driving the corresponding portion of the gear, which has a larger diameter as well. Such of unique feature of ZAKGEAR wormoid is missing in the classic Globoid gear and results in higher sliding velocities and higher friction drug on the classic globoid gear. An experienced in the art engineer would immediately derive possible design advantages of the wormoid gear. For example, using of the wormoid gear can significantly reduce cost of electric powered assist mechanisms that are commonly used on modern automobiles. Because of the higher driving efficiency, wormoid gear set can be designed with increase ration and provide the same driving efficiency as the original worm or double enveloping worm gear. For example NSK worm gear 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 ZAKGEAR would be capable to increase the ratio up to 30:1 and the torque on the gear up to 150 Hm without increase of the center distance between the gear and the pinion.

An experienced in the art professional would immediately realize the tremendous potential of using ZAKGEAR technology for improvement of the automotive electric powered actuation steering system.

Firstly, with 50% increase of the ration wormoid steering system would allow to use a smaller and lower cost electric motor, which would rotate at 50% higher RPM

Secondly, the cost of the electric controls will be significantly reduces because of 50% higher RPM electric motor would require about 50% lower operating current.

Thirdly, increased load capacity would allow to apply electric powered steering technology, incorporated low cost plastic gears, to larger cars such as pickup trucks and SUVs.

Picture 8. ZAKGEAR 3-d CAD model of a reduced performance skew axis enveloping gear.

 

In addition to the improvement of the driving performance and cost reduction ZAKGEAR wormoid steering column design can be more compact in packaging. Because of the skew axis the electric motor can be placed closer to the middle of the steering column.

The other good example of the advantage to use ZAKGEAR methodology is Ultra Globoid Gear development which was conducted in 2001 under a contract with New Venture Gear. While the practical test results of the novel Ultra Globoid Gear design has not been disclosed, ZAKGEAR was the primary supplier of the design and analyses software, which made it possible production and validation of the gear.

Picture 9. ZAKGEAR developed a complete software package for simulation of the 3-dimentional model and tooth contact of Ultra Globoid Gear

ZAKGEAR capabilities and services in relation to Globoid (Double Enveloping worm) gear:

Picture 10. ZAKGEAR Globoidal pinion manufactured by grinding.

Home page: www.zakgear.com