July 24, 2016 at 1:26 pm #2454
Had it ever been considered to use a variable pulley primary drive on the belt drive models, e.g. one of these http://www.hoffcocomet.com/EpiphanyWeb/flexpage.aspx?ID=75 It would be possible to insert a spacer bush into the driver pulley, thus disabling the initial clutch action of these units but keeping the speed variability aspect, This means engine braking would be retained at all times. My reasoning is to allow the tractor under light load to travel faster without having to rev the engine to 3600 rpm. The units can be made ‘torque responsive’ meaning that a load on the blade will over ride the variation out to higher speed that would occur as engine revs increase. Thus the machine may run @ 3.5 mph lightly loaded while the engine revs are limited to say 3000. As load comes on the drive, it varies back to about 1.4 mph @ 2100 engine revs (peak torque). This is similar to the wet torque converter performance on the old IH TD9 . I admit that a variator under manual control would be ideal if possible – the early Bobcat skid steers used this, with the directional clutches downstream, – as in this case. I am in no way connected to Comet, there may be other makers of these pulleys.August 9, 2016 at 6:25 pm #2532
Hi Peter, can you send us the correct link, the url you attached will not open.August 15, 2016 at 9:31 pm #2607
This is a link to Comet’s home page http://www.hoffcocomet.com/EpiphanyWeb/FlexPage.aspx?ID=1 – hope it worksOctober 7, 2017 at 5:35 pm #5084
I realise that the Comet may be far from ideal as it is not under manual control. The simplest of these below have one fixed shaft variable diameter driven pulley & a prime mover that moves in & out on rails to take up belt slack. A secondary drive for a hydraulic pump is possible by mounting a bracket to carry it on the engine’s SAE bolt circle, & having a double fixed dia pulley on the engine. Hoses & wires going to the engine allow movement back & forth of this engine. This would need very little modification to the existing set up. An alternative is the fixed centre drive (again under manual control) is also shown http://www.speedvariablepulley.com/variable-speed-drives.htmlJuly 21, 2018 at 5:21 pm #5989
Came up with an alternative idea, the use of these 12v electrical clutches on both the forward travel drive shaft & chain tensioning sprocket stub shaft (both of these rotate the same way) using an optional different pulley size on each clutch. Thus drive from the engine now can be hi or lo gear – dependent on which clutch is electrically energised. (The chain drive still links forward & reverse shafts & tensioning stub shaft as at present) Belt from engine loops round both clutches & engine pulley. Again idea proven on smallest pre hydro Bobcat skid steers late 1970’s Electric clutches do not have to engage under load as downstream existing forward / reverse belt drive may be in neutral, so long lived
August 22, 2018 at 10:13 am #6005
- This reply was modified 2 months ago by Peter Edwards.
This link is from a guy using comet drives on a Cushman scooter, several paragraphs down there is much info & graphs of how they work. They are at 2.45 : 1 reduction @ 2400 rpm, & unity or 1 : 1 @ 3600 rpm. Interestingly as the load lightens the drive stays in higher gear even as engine revs drop. They do incorporate a ‘clutch take up action’ of the belt at very low revs. I suspect that this could be tuned out with washers / spacers to allow constant but variable primary drive, as there are secondary directional clutches downstream, thus retaining engine braking
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