Two-directional Overrunning Device for Front Driving Wheels
Page 35
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New Hardy Spicer Clutch for Incorporation in Road wheel Hubs which Autorrlatically Transinfts, Forwards or Rearwards, Only Outward Torque
BROAbLY, it can be said that two wheel drive adequate for conditions under which all the ratios provided by the gearbox are suitable, except first and reverse. Therefore; when the front wheels are used as a means for supplementary traction, it is, desirable to incorporate in the trans,' mission mechanism some device which ensures that they run idly, in respect-. of their driving gear, when the extra • adhesion is not needed.
One may roughly define the conditions under which this additional grip is needed as those obtaining when the torque applied to . the. road wheels exceeds a figure determined by the product of the turning force exerted by the engine at more than moderate throttle opening and. the ratio afforded by the first or reverse gearing. .
This object can, of course; be achieved by incorporating in the forward transmission _a means for
breaking the drive at dog clutch, for example, in the distribution box—but even with such a :coqpling• disengaged, the front-axle :driving.. mechanism: inust still continue to be driven round by the road wheels.
However, by using a free-wheel which is built into each of the front
hubs, this disadvantage is removed, and one of the problems facing designers of four-wheel-drive chassis is solved..- Such -.U., device has recently . been des,igne.d by • Hardy, Spicer andCo., Ltd.;'Witton, Birmingham, inventOr of the raecha.rdsin' illustrated in the acebtnpanying diagrams. An outstanding 'feature is that it transmits.. torque in either direction of rotation, r when applied from the inner member to the outer; but does not react in any such way to power coming from the outer member that might otherwise ,be conveyed to the inner; instead itallows the-outer, member to idle, that is, to ruh freely on the inner member. It will he observed that the axle, 'half-shaft carries a' 'splined sleeve (2.) Which is also externally 'splinedas at: 4—to suit'a fui-ther sleeve (1). 'These two partsform the inner member of the clutch _ Upon sleeve 1 there is a ring of rollers,' retaineda cage, .and these are: surrounded by an Outer. race of ordinary design housed in the road wheel "hub. Wheri.no drive is transmittedby the ..lcialOhaft, the ,..perer rnember Can'. rotal6 Ireaiy upon the inner,
The essence of the scheme is that
race sleeve 1 has in it a helidal split at point 3, so that ry.rien drive i applied to it by sleeve 2, the' sPlit is opened and the rollers are jammed solid. Thu*a drive is established. When under no external infltience, the split sleeve . tends slightly to COntract; therefore, in its natural position, it offers .nri" -hindrance to the free running of the rollers. However, there is presumably, sufficient load to afford the resistance required, where overrunning • ceases add driving begins, to retard the _ rotation -of' the race (1) and cause' , the splines (4) to exert their influence and expand the sleeve.
Tt • is of note that, the respective ,setions—overr tinning and driving—are wholly .automatic and quite independent, of rotational. direction. . The device is intended to be used .as, supplementary component to , a distribution-box clutch, but it can, obviously be employed alone. .inanost. cases, the drive to ..the front wheels will bc..engaged only when first or reverse
gears are brought into action.' •
A fully detailed, description . einbocliecl in -recently' peiblished .patent sp'eciiication No, 541-,044, copies of which are obtainable from II.M. Stationery Office, price ls.