Final Drive Centre

Camshaft

RV / Camshaft / Engaging Pin.

This type of gearbox is probably the most complex fitted to modern excavators. The gearbox is usually marked Hi-Dash although other manufacturers produce similar products. We are uncertain of the history of these gearboxes although we have had reports of similar devices being produced in England in the 1920's and 30's.

	The drive starts with a sun gear driving 3 planetary gears.
	Instead of the planetary gears engaging an outer annulus gear they turn 3 camshafts that are mounted equally around the centre axis.
	Each camshaft has 2 lobes. There are two large flat 'gears' each with 3 engaging holes. Both 'gears' are mounted on the camshafts, one on the outermost camshaft lobes and the other on the inner. The result is that the two 'gears' rotate eccentrically with respect to each other and with respect to the centre-line of the gearbox.
	As the camshafts are turned by the planetary gears the flat 'gears' appear to rotate in an eccentric manner within the gearboxes, in fact they don't rotate at all.
	As the flat 'gears' 'rotate' they progressively engage and disengage with pins located in the hub casing. Because the 2 plate 'gears' are eccentric from each other they engage and disengage the pins in turn. The apparent rotation of the plate 'gears' therefore turns the hub.
	The above is very complicated to explain, but please call in and we will show you how it works.

Repairs:

These types of gearboxes are complex to work on; they require specialist knowledge and tools. Watch out for:

	Any wear on any and all bearing surfaces.
	Metal - metal seal damage
	Loose or damaged retaining bolts, these must be replaced.
	Damage to the hub.
	Centre seal and shaft damage.
	Reassembly; if you are unsure don't do it. We have seen gearboxes with 90% new parts destroyed in minutes!

Advantages / Disadvantages

	This arrangement is generally robust but requires regular oil changing.
	Most parts are available.
	The gearboxes require specialist repairs to guarantee longevity.

There are a lot of other names and terms used for these gearboxes and parts; you may find:- Flat Plate Gears, RV or R.V. Gears, Hi Dash and Walking Plate Gears. Teijin Seiki also use the term or Rotary Vector with Harmonic Drive also appearing from time to time.

If you open your gearbox to find 3 large bolts holding the parts in place it is probably one of these type.

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