Fitting three into one

The e.PM range of right-angle gear drives share a three-in-one casing and a bewildering array of shared components across the range.

Film fans may remember Ian Faith, manager of Spinal Tap from the eponymous film; a man who kept the machinery of the group turning whilst the band took all the glory.

A tenuous analogy perhaps, but gears are the managers of mechanical applications: a little staid, always in the background but essential to mechanical operation.

Bruce Dagley, engineering director of Renold Gear, is the first to admit that the world of gears isn’t that dynamic, although his company did generate a ripple of excitement at this year’s Hannover Fair when it formally released the e.PM Series of right angle gear drives.

What sets the e.PM Series apart from its peers is that Renold has developed a modular range of gear drives sharing a common ‘three-in-one’ casing while also using as many ‘shared’ components as possible across single worm, helical worm and bevel/helical gearing variants.

‘For the three ranges there’s very few parts,’ says Dagley. ‘The worm ratios in the helical worm have been cut to two per size, so across the sizes – 35 up to 80 – there are only 12 different worm and wheel ratios. That’s a major reduction of parts, making for better availability to customers.’

The e.PM Series is available in three variants: the PW single-worm drive (12 standard ratios from 5:1 to 70:1, with a maximum output of 4700Nm), PH helical-worm combination (16:1 to 333:1 ratio range, maximum torque 8100Nm) and the PB helical-bevel-helical arrangement (16:1 to 160:1 ratio range, maximum torque 12000Nm).

‘We set out to maximise the ratio reduction we got from the first pair of helical gears so that we could have lower ratios on the second stages, whether it was worm, bevel or helical,’ says Dagley.

‘Its an engineering fact that if you have slower speeds and lower ratios you get high torques through your second stage gear. By taking more ratio out of the high speed end we could get more torque out on the second stage gearing.’

Each variant is available in six sizes, from 90mm (3.5in) to 200mm (8in) centres, with a hollow bore or output shaft, and as a speed reducer or motorised unit with input power from 0.55kW to 60kW.

A key feature of the range is a new compact input housing and an arrangement enabling the plug-in fitting of IEC motors to a completely sealed drive. Also, all models can be fitted with a wide range of standard accessories, including plug-in output shafts, torque restraints and dry well facilities on some models.

Another user benefit is that the e.PM Series is predicted to give a 52% increase in performance ratings over existing gear drives and, in many cases, this should give the option of choosing a smaller gear than before for exactly the same application.

‘The 52% increase in performance rating is calculated on the basis of the different worm ratio for the same overall ratio between the old helical worm range (PowerMaster) and the new ePH,’ says Dagley. ‘Because we’ve upped the ratio on the first pair of gears we can lower the ratio on the second pair of gears to get the same overall ratio.

‘Because we’re lowering the ratio we can get more torque through at the second stage, therefore we can calculate that we have up to 52% additional performance,’ he adds.

As well as the e.PM Series of right angle drives, the Renold Modular range will soon include the e.RP Series of in-line drives and the e.SM Series of parallel drives. ‘The e.PM series doesn’t mark the difference between a propeller driven aircraft and a supersonic jet because there’s not a lot like that in gearing,’ says Dagley modestly.

‘Having said that we do believe that the e.PM Series is a ‘first’ because we’ve dramatically reduced the number of components and we’ve thought about shared components across the three ranges and because it’s part of a modular range that also includes coaxial helical and possibly, eventually shaft mounted helical.’

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