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Latest Air Disc Brake Innovation

Youfin has recently developed a heavy duty air disc brake caliper featuring linearly guided, non-rocking tappets that deliver radial pad pressure distribution that is more uniform throughout the entire clamping stroke. Unlike conventional designs, access to machining these guides does not require separating the housing into two or more parts, thereby achieving both high housing strength and stiffness at a low manufacturing cost.

Issues With Rocking Tappet
(Diagram drawn not to scale)

As the output arm of the eccentric lever swings through an arc during actuation, the inboard end of the tappet traverses up and down. Combining with a "point" support of a narrow guide bearing at the outboard end, this produces a rocking movement in the tappet as it advances forward to increase clamp.

Issues With Over-Constrained Lever Mechanism That Is Fitted With Tappet Guides

This design has a fully guided tappet, but the lever is over-constrained which forces the lever pivot to both roll and slip at its seat under load. As a result, this produces heavy scuffing of lever pivot and its seat reducing the apply clamp efficiency and causing damage to the lever pivot interface. The over-constraint also puts a high reaction load on guide surfaces further increasing clamping loss and reducing wear life of the guides. Beside, this design requires a two-piece housing construction to allow access to machining of the guide surfaces. This extra machining and joining add to the manufacturing cost and potentially reduces housing stiffness and durability.

Youfin’s Solution (Schematics)

Youfin’s unique one-piece caliper housing design saves unnecessary machining and joining while maximizing housing strength and stiffness. Machining of guide surfaces is accessed from a pair of holes at the bottom of the caliper housing. The plugs for the holes also form a part of the linear guide. The pivoting shaft is now free to roll as needed without creating antagonistic forces that chew up clamp efficiency and component wear life.

Experimental Data on Pressure Distribution  

Summary Advantages Of Youfin’s Improved Air Disc Brake

1. Tappet(s) fully guided to move linearly, does not rock as it advances

2. More uniform radial pad pressure distribution

3. Minimize the generation of uneven pad wear such as radial taper wear and/or “fish back” profile

4. Minimize the generation of brakes off residual drag as radial pad taper tends to de-stabilize running clearance

5. Minimize concentration of heat flux, resists fade and maximize performance

6. More consistent effective clamp radius

7. More predictable and linear output

8. High clamping efficiency as kinematic of apply mechanism is not over-constrained

9. Highly loaded lever pivoting mechanism is free to roll and not slide hence minimizes wear and tear

10. One-piece housing with no structural joints improves stiffness and durability

11. Lower part-count design reduces manufacturing costs

12. Unique patented housing design allows easy access to machining internal guide surfaces

13. Applicable to most existing caliper designs including single and twin tappet configurations

 

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