Planetary Gear Drives - a brief theory

A large family of gear arrangements is categorised under the general name of EPICYCLIC GEARING, An Epicyclic gear train has a central SUN gear, several PLANET gears meshing with & spaced around the Sun gear and a RING gear, also referred as an ANNULUS gear. Sun & Planet gears are externally toothed while Ring gear is internally toothed. The name Epicyclic comes from the fact that the points on the Planet trace epicycloidal curves in space. Stationery or rotating Sun gear, Planet gears and Ring gear result in different Epicyclic gear arrangements, one of them is termed as PLANETARY GEAR TRAIN.

A typical Planetary Gear Train arrangement is depicted below.

The speed reduction ratio of a Planetary transmission is function of the number of teeth on the Sun gear (Zs) and the number of teeth on the Ring gear (Zr) and is given by the equation (Zr/Zs) +1. A single-stage Planetary gear train normally gives a reduction ratio from 3:1 to 10:1. For obtaining higher reduction ratios multiple stages of Planetary configurations are adopted.

Sun gear acts as an input to the gear train, three Planets connected to the common member called PLANET CARRIER acts as output of the gear train, and a fixed Ring gear acts as body or housing of the gear train.

Turning of Sun gear results in movement of Planet gears on their own axis as well as around the Sun gear when Ring gear acts as a stationary element. The motion of these Planet gears are very similar to the motion of planets in the Solar System, and so the name PLANETARY GEAR TRANSMISSION.

By virtue of this typical gear train arrangement, Planetary Gear Drives are of co-axial configuration having input & output shafts rotating in the same direction.

Generally three Planet configuration is adopted, although any number of Planets can be considered. Higher number of Planet gears offers advantage of reduced teeth load, but such configurations suffer from certain manufacturing complexities, and hence are not very popular for general purpose Planetary Transmissions.

Use of the spur gears is more common for general purpose Planetary Gear Transmissions, while some customised high-speed Planetary Transmissions have Helical Gears.

Kinematic Diagram of a typical three-stage Planetary Gear Transmission

Stage I comprises of 18T Sun gear, 42T Planet gears & 102T Ring gear, which gives speed reduction ratio of 6.667:1.

Output of Stage I acts as input to Stage II having 17T Sun gear, 25T Planet gears & 67T Ring gear resulting in further reduction ratio of 4.941:1

Output of Stage II acts as input to Stage III having 17T Sun gear, 18T Planet gears & 52T Ring gear resulting in further more reduction ratio of 4.059:1.

The combined speed reduction ratio of these three stages works out to be (6.667 x 4.941 x 4.059} 133.71 :1.

Detailed analysis of the forces acting on the gear meshes shows that output torque of each Stage is ratio times its input torque. In other words, each Stage multiplies the torque. The above three-stage Planetary Gear Transmission gives output torque which is 133.71 times the input torque, assuming no transmission losses.

Kinematic Diagram of a typical three-stage Planetary Gear Transmission

SPH Series Gear Drives Exclusively Customised for Sugar Plant Equipment

INNOTRANS SPH Series Gear Drives are exclusively developed for the Crystallisers, Strike Receivers & allied equipment in Sugar Plants and Sugar Refineries.

These Gear Drives have a unique configuration of a Helical gear pair and multi-stage Planetary gears, all housed in a single housing to form a compact low-speed & high-torque gear transmission. A multi-stage Planetary gear train is directly flanged onto the housing that accommedates helical gear pair. Electric Motor is flanged onto the input end of the multi-stage Planetary gear train.

Shaft mounted configuration of these Gear Drives eliminates bulky foundations, couplings, base frame, etc., normally required for general purpose Gear boxes. Through & through hollow output shaft of this Gear Drive slides over the driven shaft & gets axially locked to it by a gib head taper key.

A detachable manual handle facilitates easy manual rotation of the driven shaft by manually turning non-driving end shaft of the motor. Such manual operation is sometimes called for at the time of power changeovers and also during off-season maintenance work on the rotary elements of the driven equipment.

A Torque Arrester supplied along with the Gear Drive is required to be bolted onto the machine structure for taking reaction force of the Drive.

Key Features

  • High Efficiency transmission
  • Simplified Installation - Direct mounting onto the driven shaft eliminating coupling, shrink disc, mounting base structure, etc.
  • Use of Rolling Bearings results in extended service life.
  • Common Oil Sump adequately lubricates all rotary elements, ease of oil filling & oil draining.
  • Double-lip Oil Seals on output shaft eliminate ingress of water, fine dust, etc. Oil Seal on input shaft prevents oil contact with the Motor.
  • Easy manual operation through a detachable handle at non-driving end of the Motor’s shaft.
  • Higher Thermal Rating as compared to standard Planetary Gear Boxes — no de-rating on thermal capacity is needed upto 60 deg. C ambient temperature.

By INNOTRANS SPH Series Gear Drives - Standard Dimensions

SPH Series Gear Drives - an ideal replacement for conventional Worm Drives

SPH Series Gear Drives are ideal replacement for the conventional Worm gear drive systems generally employed for Crystallisers and similar low-speed high-torque equipment in Sugar Plants & Sugar Refineries.

The conventional Worm gear drive system comprises of a foot mounted motor driving a single stage Worm gear box through a flexible coupling, both mounted onto a common bed plate. This single stage Worm gear box is further coupled to the open type Worm shaft which in turn drives open type Worm wheel mounted onto the driven shaft as shown below.

Conventional Worm gear drive system suffers from the following major disadvantages.

  • High power consumption due to lower efficiency, the combined efficiency can be as low as 25%.
  • Frequent replacement of worm gearings due to high sliding between shaft mounted worm wheel & structure mounted worm shaft.
  • High lubrication consumption, frequent topping up of oil due to oil spillages.
  • Frequent replacement of bearings due to Couplings' misalignment & contaminated lubricant.
  • Higher cost of routine maintenance & house keeping.
  • Cumbersome manual operation during power off conditions.
  • Higher thrust loads on the driven shaft severely affecting life of support bearings gland packing.
SPH Series Gear Drives

Replace conventional Worm gear drive system with INNOTRANS SPH Series Gear Drives & get these benefits.

  • + Power saving of 50-70%
  • Lubrication consumption down by 70-80%
  • Longer maintenance free periods, over 80% reduction in routine maintenance costs.
  • Clean surroundings
  • Ease of manual operation during power-off conditions
  • Longer life of the driven shafts’ support bearings & gland packing.

SPH Series Gear Drives - Rating Chart

The following table indicates Output Torque rating, hollow output shaft's bore size & input power ratings for each Unit. Rated Output Torque indicates continuous duty rating while Peak Output Torque ratings are for handling starting & short time load transient conditions only.

Rated (Peak) Nm
Max. Dia x Length
Input Power
Nominal Output speed
SPH-07 13,400 (26,800) 110 x 185mm L 3.7kW/3.7RPM
SPH-09 17,400 (34,800) 130 x 194mm L 3.7kW/2.5RPM
SPH-13 24,700 (49,400) 150 x 230mm L 5.5kW/2.5RPM
SPH-20 41,500 (83,000) 160 x 250mm L 7.5kW/2RPM
SPH-30 63,100 (126,200) 185 x 300mm L 11kW/2RPM
SPH-50 87,600 (175,200) 210 x 330mm L 7.5kW/1RPM
SPH-60 138,300 (276,300) 230 x 390mm L 11kW/1RPM
SPH-70 186,500 (373,000) 240 x 440mm L 15kW/1RPM
SPH-80 260,800 (521,000) 250 x 490mm L 22kW/1RPM