Claw circuit

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The dog clutch is a term used in mechanical engineering and, in particular, vehicle technology .

With dog gear shifting, the gear of a gear, which is immovably but freely rotatable on the gear shaft, is connected to the shaft when shifting with a dog clutch (by axially moving a dog ring) and can then transmit a torque. In the case of a sliding gear , the gears are non-rotatably but displaceably seated on a spline shaft ; in the case of draw-wedge switching, a draw-wedge is axially displaced inside the loose gear shaft , which is usually double-grooved.

The dog clutch can transmit a higher torque than the draw wedge clutch; the disadvantage is the larger width of a dog gear and the resulting higher weight. Gearboxes with dog gears are more compact than those with sliding gears and can be better designed with helical gearing . Older vehicle transmissions often have both: Reverse and 1st gear with straight-toothed sliding gears, higher gears with helical gears and dog gears or synchronization .

The differences can be seen in the small motorcycles of the 1970s: companies such as Hercules , DKW and Zündapp built draw-key transmissions; however, the competition from Kreidler , Zündapp (some models in the 1980s) and Puch , regarded as “noble”, built in the claw mechanisms, which were regarded as more robust.

Fig. 1, two-speed dog clutch, principle
Fig. 2, two-speed dog clutch, simplified. Second course by connecting through
Fig. 3, three-speed dog clutch with reverse gear
Photo 4, claw

Another fundamental difference lies in the possible gear sequence: Draw-key gears only allow sequential gear changes. (In order to get from fifth to first gear, the draw key must be moved once along the entire groove.) Shift claws, on the other hand, can in principle also be freely moved into any position, provided that their external actuation via the shift drums or other actuation mechanisms allows this. This is not implemented in mopeds and mopeds, i. H. the claw gears work sequentially because of the shift drum design, but in motorcycles (partly) and in automobile transmissions, the free gear selection for claw gears is implemented: gear changes can also be made from e.g. B. happen fourth gear in the first.

Description of the sketches

Description of a basic two-speed claw gear:

  1. Gear input shaft with fixed gear with claws on the face
  2. Gearbox auxiliary shaft with gear 4 that meshes with the gear on the input shaft
  3. Transmission output shaft, longitudinally grooved
  4. Gear sets with helical teeth
  5. Gear, rotatable on the output shaft, but not shiftable
  6. Shift claw, axially displaceable but not rotatable (guided in longitudinal groove)
  7. Shift fork with operating rod. Grips in the groove of the switching claw and moves the claw axially:

to the right to gear 5 → gear reduction, 1st gear, or to the left, claw on the input shaft, output shaft rotates just as fast as input shaft → 2nd gear

In the second picture a simplified representation of a two-speed transmission; for the slow connection, the torque flow goes through the auxiliary shaft. For the "fast" connection, the input and output shafts are coupled at the front (1: 1 speed), the gears and the auxiliary shaft run idle (decoupling mechanism not shown).

The third picture shows a simple three-speed transmission with reverse gear. The right claw switches between 1 and R (red), i.e. H. between first and reverse gear. Reverse travel is possible because the third central R-wheel (with its own bearing of the shaft) causes a reversal of the direction of rotation (with the other claw in the middle). In the middle position of the shift dog for 1 + R, the left shift dog can switch between second and third gear.

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