Let's introduce the internal transmission of high-end bicycles. Among the bicycle internal transmissions (internal speed-changing hubs), the truly high, large and high-speed ones are the German Rohloff 14 internal transmission and the Sothis 14 internal transmission introduced by Hong Kong Fuhui Precision. The weight of these two transmissions is about 1.7kg, but the specific width of Sotis is slightly higher than that of Rokhlov. The former is 539.7% and the latter is 526%, which exceeds the traditional 27-speed external transmission, followed by Shimano's 1 1 speed (the speed ratio width is 409%, and the flexibility and durability of the structure are different from the former two). These three kinds of speed changes are gear shifting, which work by using the principle of planetary gear train transmission, and there are multiple groups of compound planetary gear trains inside by external force transmission.
Variable speed principle of planetary gear train;
The planetary gear mechanism has three relatively rotatable moving parts: sun gear, planet carrier and gear ring. A set of planetary gear trains can realize four different gear combinations:
① Low-grade sun gear is active, the planet carrier is passive, and the gear ring does not move.
(2) The neutral sun gear does not move, the planet carrier is passive, and the gear ring is active.
(3) In high gear (overdrive), the sun gear is stationary, the planet carrier is active, and the ring gear is passive.
(4) In reverse gear, sun gear is active, the planet carrier is stationary, and the gear ring is passive.
The transmission is in neutral when all moving parts are unconstrained.
Planetary gear transmission usually consists of two or three groups of planetary gear mechanisms, and different gears are realized by controlling the combination of the above moving parts through multiple clutches.
Besides, the representative of the present continuously variable transmission "nuvinci N360" uses eight steel balls to rotate around the main shaft, and the friction on both sides of the steel balls drives the power. The shift lever moves in series in the spindle to drive eight steel balls to move between the driving side and the driven side, and the contact friction surfaces between the steel balls and the two sides will change, so as to achieve the purpose of speed change, so the speed change has no polarity, but this principle leads to its low transmission efficiency, not too long service life, and the speed change ratio width is 360%.
Finally, the automatic gear is a slightly lower-end internal transmission device, with only three or four gears. Its principle is mainly based on the principle of centrifugal force. A plurality of centrifugal steel balls are evenly distributed around the main shaft, the outer sides of the steel balls are pressed by springs, the central raceway of the steel balls is on a conical sleeve which can move in series, and one end of the conical sleeve is subjected to the spring force and the pressure of the centrifugal steel balls, thus achieving position balance. When the wheel rotates, centrifugal force changes the pressure of the steel ball on the taper sleeve and breaks the stress balance of the taper sleeve. When the balance force is destroyed to a certain extent, the position of the taper sleeve will change, thus pushing the internal gear to shift gears to achieve the purpose of speed change, so that the transmission speed ratio width is not high and the structure is simple.