Cam & Pawl Differential
Cam & Pawl Differential
First of all, I came to think of them as not being differentials, in the purest sense of the word, but rather as spools which allow a certain amount of slippage on the inner wheel when neccessary. In a sense that pawls that engage the lobes will transmit torque to both sided equally (and the way I see it, with minimum to no loss at all), but if excessive 'drag' occures on one cam, it will be allowed to slip (with increased friction and other losses on that side alone). Sort of like spool which can act as a differential when forced to. (This in a way may be in consistency with one of the earliest descriptions I found, by Pomeroy, which reports them having great losses in low speed corners- which did not matter much with overpowered beasts of the day, and was even supposed to be beneficial to handling by making cars less throttle sensitive, and hence less prone to spin out when applying 600BHP through skinny tyres in hairpins).
Now, this does make sense to me, but is also a source of confusion. That would mean the diff will have understeering influence on the car, up to the point where differential action occurs and it switches to contributing to the oversteer. Which should be, first of all, opposite of how I percieve other LSDs behave- being neutral/oversteery in normal operation and progressing to understeering influence as they lock-up. It seems to big an issue not to be picked up on by somebody- from Stokes who is transmission guy, or say Carroll Smith whose drivers might have noticed it, esp. when authors speak of LSD more or less abruptly coming into action. (Sorry for introducing handling and stuff to the proceedings, but I feel the differentials are usually 'underprivileged' components- chassis books rarely make a mention of their influence, while transmission books reduce them to the perception of few gears attached to the bits that matter. I choose to take interdisciplinary approach, with one inseparable from other.)
Another thing that I would be keen to learn more about is the lobe design. Almost no mention of it is to be found in literature, IIRC save one source which implied black art being used in conjuction with trial and error method evolving to the current design (again, no shape of lobes mentioned- only 13 lobes on outter cam, 11 on inner and 8 pawls)...
Any info, or your thoughts on the subject would be most welcome. Thanks in advance.