I hope it would be OK if I asked a few questions about cam & pawl differentials. I've always sort of fancied them, but am not sure I fully understand how those infernal contraptions work... And not much in the way of resources is available for them- an odd mention here or there, and the best one can hope for is description of their workings (but those often also include discrepancies, even conflicting 'findings', &c). While Stokes is rather complimentary about them, the rest of sources describe them with almost anything short of brutish, unreliable, nuisance, and so forth... But if they had lasted in Grand Prix and Formula 1 racing for almost 60 years (they were AFAIK introduced by Mercedes or Auto Union in early '30ies, and Stokes reports them still being used in F1 in '90ies) would suggest some merit in the design which the rest of authors usualy fail to register.
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.
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.
