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Re: Farmall H live hydraulics saga continues...
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Posted by Bob M on January 10, 2003 at 08:43:21 from (165.170.128.68):
In Reply to: Farmall H live hydraulics saga continues... posted by Steven@nd on January 09, 2003 at 16:27:53:
A few comments from a mechanical engineer's perspective (which incidentally I happen to be...)
1 - Driving the pump thru a simple universal joint operating at an angle can work. But has a problem: Due to the single joint setup, the pump will undergo a significant sinusiodal variation in output shaft RPM twice each shaft revolution. The sharper the angle, the greater the variation. (Anyone who has turned a corner pulling a PTO-driven bush hog has experienced this...)
Anyway assuming a joint angle of 20 degrees (eyeball estimate), and limiting the angular acceleration to a "reasonable" level (<1,000 radian/sec**2 for you engineers) a quick calculation says the pump shaft should not exceed about 850 RPM. And even at this level there will be significant radial (side) stress on both the U-joint and the pump input shaft bearing. So as soon as you get ANY wear in either the U-joint or pump bearing, it will become rapidly VERY noisey and be well on it's way to self-destruction.
2 - You could drive the pump through some sort of CV joint to eliminate the sinusoidal speed variation from the cross-joint universal. However the matter of radial load on both the CV joint and the pump bearings will remain. Also unless a high quality and fully sealed CV joint is utilized (translation: expen$ive!), the joint will suffer from a short life.
3 - A better plan from a cost/life perspective is to belt the pump to the crankshaft via a timing belt or synchronous (Polychain, etc) drive. Synchronous belt drives are cheap, require no lubrication, are reasonably tolerant of dirt, and will handle huge amounts of power (e.g. Harley -Davidson final drives).
To the issue of the radial load imposed on the front crank bearing from a synchronous belt-driven pump, the load will be only modestly higher than the radial load imposed by the timing gears onto the crank by an OEM live (distributor) pump. Also if you look at the combustion and dynamic loads already carried by the crank mains, the additional load imposed by a synchronous belt drive pump will be inconsequential. My 2 cents! ...Bob M
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