The Change Of Bicycle Bearing Support Structure
For the early cassette type loose-beaded drums, the support points of the left and right bearings are often far apart, very close to the position of the fork hooks, and the shaft center is steel, and the design has considerable redundancy, so few people Worry about its strength and longevity.
Figure 1 A typical Shimano ball hub with its right-hand bearing placed on the right side of the tower. The shaft shell transmits force to the bearing through a steel or titanium (XTR and DURA-ACE grade) support housing. .
In this configuration, the support force on the right side and the driving force from the tower base are transmitted to the shaft housing through the same component, that is, the support housing (the support hull component in the figure) integrated in the tower base system. Up. Because the internal space of the tower base is small, the entire ratchet system and the tower base bearing must be accommodated on the outside of the support housing, and the thickness thereof is limited, so that it can only be made of steel or titanium alloy, and it is difficult to reduce the weight.
In order to simplify the structure and reduce the weight, most of the hubs now use a rather simple structure, that is, to cancel the support shell, and directly place the right support bearing on the right side of the axle housing.
Figure 2 The simplified hub of the support structure – you can see that the right bearing is so close to the centerline that it is subjected to a load of more than 90%.
The hub that uses this structure has a huge advantage in terms of ease, the structure is very simple, and it can be made entirely of easy-to-process aluminum. Its design and production have become so technically lacking, even in China. The piles of flowers that look almost exactly the same are springing up. On the other hand, the simplification of the structure also prompted the hub system to easily break through the lower limit of weight. A pair of drums of less than 200 grams is no longer a difficult task, and the dash company from the United States even made only 30/ before and after. 84 grams of incredible flower drums!
Figure 3 Incredibly lightweight – a pair of dash hubs weighing just 114g.
In addition to simplifying the structure, reducing the weight of the hub can also be achieved by using thinner (small) bearings.
Figure 4 Specifications of common bearings
As can be seen from the table above, the weight reduction effect of using a thinner (small) bearing is simply immediate. In comparison, it is much more difficult to dig some weight from the axle housing or the tower base.
However, these two methods of weight loss are essentially contradictory. The hub of the support housing is omitted, and the right bearing is so close to the centerline that it is subjected to a load of 8-9%. The shaft is also in the most severe stress conditions.
Figure 5 The bearing force on both sides of the shaft shell must satisfy the two conditions that the sum is equal to the total load and the combined moment with respect to the center point of the hub is zero. This means that the closer the right bearing is to the centerline, the greater the load it will take.
Figure 6 Simplifies the hub axis as a simply supported beam with a point force. The maximum bending moment occurs at the load loading. It can be seen that the bending moment of the beam is the largest when P is at the center.
Figure 7 Under the condition of the force, the deflection (y value in the figure) reaches the maximum value at the center point. It is easy to know that when P is at the center (ie, a=b), the deflection is the largest.
Therefore, manufacturers have to use thicker or thicker axes to meet the strength and rigidity requirements. This is also the reason why the hub of the hub has become thicker and thicker in recent years. The shaft of the 12mm caliber has become obsolete. The axis of the 15th and 17mm caliber becomes quite common. What is more, fulcrum is used on their mountain wheels. A 20mm shaft! In the era when the bearings are generally placed on both sides, the diameter of the shaft is only 10mm, directly through the entire hub, but no one is worried about their strength. Rather than saying that this is an improvement, it is better to say that this is the price that has to be paid for the sake of weight reduction.
Figure 8 The early hub of the hub is usually a shaft that runs through the entire shaft and has a uniform diameter of 10 mm from the front 9 mm. The card slot diameter of the fork hook is also this number. In the past, frame specifiers may not have thought that modern hubs would face such serious strength problems: D
Figure 9 20mm axis? I don't think there is anything worth promoting.
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