Shimano Nexus Alfine 8 speed How it works

the Shimano Nexus and elfin a8 speed gear hubs have become a popular choice among recreational commuter and utility cyclists beyond the clean look and simple chain line they offer several benefits over comparable derailleur systems a single shifter with sequentially numbered gears no overlap to worry about as with dual derailleur systems the ability to shift while stopped and the simple set it and forget at shifting system make it very appealing for many riders most riders are content to remain blissfully ignorant about the mechanical workings inside the hub but for those with inquiring minds that wonder just how does this thing work I now offer this video the Shimano Nexus elfin a 8-speed how it works like all internally geared bicycle hubs the Shimano elfine a nexus works on the planetary or epicyclic gearing principle the basic planetary gear train consists of a Sun gear planetary gears which revolve about the Sun gear and are mounted in a cage or a carrier and the ring gear which has gear teeth on its inner circumference and meshes with the planetary gears in order to function one of these units must be the input or the means by which the power is delivered into the assembly an output which is the component which transmits the final drive ratio to the wheel and one of the components must be fixed or reactionary that means it's held in place so that the other components can react against it for bicycle gear hub applications the Sun gear is always the reactionary gear now let's take a look at how the direction of power flow through the hub affects the relationship of ratios between input and output when the ring gear is the input and the planetary carrier is the output and the Sun gear is the fixed reactionary gear the result is under drive when the planetary carrier is the input and the ring gear is the output and the Sun gear is the fixed reactionary the result is overdrive the ratio differential is governed by the difference in size between the Sun gear and the ring gear the greater the size of the Sun gear in relationship to the ring gear the greater the differential in speed between the two this is an important point to remember we will be bringing it up later as we explore the hub so now we will take a look at how these principles are applied to achieve eight distinct Drive ratios in a nexus elfin a hub the design is essentially a four speed hub with a high end low range there is no overlap or redundant gears so the dual range doubles the four speeds to eight first a word about how the power is delivered into the internal mechanism and from there to the hub shell to power the bicycle forward the power input is by means of the COG which is driven by the chain from the pedals the COG is mounted on the driver which transmits the power into the internal mechanism by means of a roller clutch to transmit the power to a ring gear to achieve low range or a positive clutch which bypasses the lower range reduction and engages directly to the planetary carrier for a direct drive ratio the transition between low range under drive and direct drive occurs when shifting from fourth to fifth gear the power is transmitted from the internal mechanism to the hub shell by one of two additional roller clutches which of these clutches transmits the power depends on whether any of the Sun gears in the ring gear carrier are coupled to the axle by means of the rising poles or not the roller clutches consists of smooth steel rollers caged in a metal ring when power is transmitted to the clutch in a forward rotation the rollers write up ramps and are pressed against a steel track with a force great enough to create friction between the rollers and the steel track in this way power is smoothly applied and force is transmitted from one component to the other when no forward rotational power is delivered or if the driven component tries to freewheel over the roller clutch the rollers are drawn back by a spring which returns the ring to its default neutral position this allows for backpedaling or coasting now we move on to studying the power flow in each gear first we will look at the low range reduction unit which is the first stage of the power flow when the gear selector is in any of the first four gears the driver transmits power to the low range ring gear the ring gear drives a set of planetary gears which is mounted in the gear carrier the planetaries rotate about the low range Sun gear which is permanently affixed to the axle therefore the input is the ring gear and the output is the planet Aries if you remember the power flow discussion in the introduction this means that the output ratio is underdrive specifically a ratio of one revolution input to point five to seven revolutions output this ratio is constant throughout gears one through four within the gear carrier are three Sun gears of varying size and matching stepped planetary gear sets these planetaries drive a ring gear on which is mounted a roller clutch which transmits power to the hub shell going back to the introduction the larger the Sun gear in relation to the ring gear the greater the differential in speed between the units the Sun gears are engaged by means of rising Pauls which are actuated by the shifter through an actuation arm in order for power to be transmitted to the ring gear one of the Sun gears must be coupled to the axle to become the fixed reactionary gear Sun gears not couple to the axle are free to rotate and will not function as a reactionary element when the shifter is in the first gear position all three poles are retracted and none of the Sun gears are engaged this means that no power is transmitted to the ring gear so the ring gear roller clutch does not drive the hub shell in this instance the roller clutch mounted on the end of the gear carrier transmits the power to the hub shell at the 12.5 to 7 ratio when the shifter is moved to 2nd gear position the outer Paul is actuated and couples the smallest of the three Sun gears to the axle now we have a reactionary gear so power is transmitted to the ring gear at an increased speed and the roller clutch drives the hub shell the ratio between the gear carrier and the ring gear is one input revolution to one point two to three output revolutions but because of the low range reduction at the input end the compounded ratio is 1 input revolution 2.64 for output revolutions because the ring gear roller clutch is driving the hub shell at a speed greater than the speed of the gear carrier the roller clutch mounted on the carrier is being overrun by the hub shell the rollers retract and are neutralized when the shifter is moved to the third gear position the outer Paul retracts and the Center Paul Rises coupling the middle gear to the axle it now becomes the reactionary gear as I pointed out earlier the greater the size of the Sun gear in relation to the ring gear the greater the speed differential will be between the driving and the driven unit the ring gear now rotates 1.41 9 revolutions and when compounded with the low range reduction results in an input ratio of one input revolution 2.74 8 output revolutions when the shifter is moved to the fourth gear position the middle Paul retracts and the inner Paul Rises now the largest of the three Sun gears is coupled to the axle and the drive ratio between the gear carrier and the ring gear is one revolution input to one point six one five revolutions output the compounded ratio from the driver to the final output is one revolution to 0.85 one revolutions when the shifter is moved to the fifth gear position the poles are all retracted and the clutch engages the driver directly to the planetary carrier by passing the low range reduction gear here is a clip showing in greater detail how the clutch is actuated so at this stage I can explain the functioning of the high-low range selector this is the clutch which engages the driver to the gear carrier in high range and bypasses the lower range reduction unit now it consists of a ring with radial splines on the matching surface that that engages the climate carrier and there's a ring that actually is free-floating within the clutch ring and it has two tabs on those tabs ride in these slots on this cup and when you install it you have to be very careful to make sure that those tabs are engaged with those slots so the way that it works is I turn this so that the camera can see it these tabs right along this surface here as the shifter is rotated so gears one through four as it rotates these tabs move along this surface here when the shifter moves to gear number five those tabs right down that slope ramp and gears five through eight the tabs right along this lower Ridge so the spring actually pushes on the clutch and when it rides down that ramp it engages with the planet carrier and gives you your high range so I can give you a little demonstration of that by putting the clutch in the slots alright and then rotating this and when it gets to the position where fifth gear and what happened you see it drop down okay so low-range the clutches up high range the clutches down iron low range high range and that's that in fifth gear with the driver coupled directly to the planetary carrier and all three poles retracted once again there is no power flow to the output ring gear this means that the roller clutch on the planetary carrier drives the hub shell directly this results in one revolution input to one revolution output or direct drive 6th 7th and 8th gear are a repeat of 2nd 3rd and 4th without the low range reduction 6th gear is a ratio of one input revolution to one point two to three revolutions output seventh gear is one revolution input to one point four one nine output revolutions and 8th gear yields one point six one five output revolutions to one input revolution this concludes this episode I hope I have helped to demystify this unit for all of you here are some links to some of my other videos in the gear hubs demystified series I hope you will watch and enjoy them all please post your comments below thank you for watching

Channel: Dan Burkhart

Views: 1,065,612

Rating: 4.6638227 out of 5

Keywords: Shimano, IGH, internal gear, epicyclic gear, planetary gear, nexus, Alfine, bicycle, city bike, transmission, bike lane, commuter bicycle, gear shifting, bicycle repair, bicycle wheel building, gearhub, Sturmey Archer, Dan Burkhart, Waterfront Wheelshop, 2wagondragon, cargo bike, Toronto, bike trail, bike path, bicycle mechanic, bicycle gears, how it works, how stuff works, recreation, 8 speed, eight speed, 3 speed, three speed, mechanism

Id: _Q5iEywX3yM

Length: 13min 57sec (837 seconds)

Published: Sun Apr 24 2016