The Effect of the Running Clearance to the Braking Force

Abstract

A typical air disc brake generates the braking torque by friction between rotor and pads located on both sides of the rotor. Friction causes pad and rotor to wear every time brakes are applied. As a result, a gap called running clearance is created between pads and rotor. Automatic adjuster compensates for the wear and keep the running clearance stable. If any malfunction occurs in the automatic adjuster, brake will not self-adjust and the gap will get larger. In this study, the effect of the running clearances to the braking performance was analyzed. Braking forces caused by friction between brake pads and rotor were calculated from air disc brake’s mathematical model for different running clearances and compared with the experimental results. Both the calculated and experimental results indicate that the braking force is affected from running clearance. Air chamber stroke increases proportionally as the running clearance increase but it has a physical limit. The mechanical advantage ratio of operating shaft is higher at large stroke values but it is observed that the air chamber, which provides the input force is inversely affected by the clearance after 50mm pushrod stroke. Excessive brake gap combined with high deflections caused by high input pressures overcome the operating shaft ratio increase and reduce the output force of the brake.

Keywords

• Air disc brake
• automatic adjuster
• braking force
• running clearance

References

1. [1] Limpert, R. Brake design and safety Third Edition, SAE; 2011.
2. [2] Day AJ, Bryant D. Braking of road vehicles. Butterworth-Heinemann; 2022 Mar 21.
3. [3] Tagesson K. Truck steering system and driver interaction. Chalmers Tekniska Hogskola (Sweden); 2014.
4. [4] Tagesson K, Cole D. Advanced emergency braking under split friction conditions and the influence of a destabilising steering wheel torque. Vehicle system dynamics. 2017 Jul 3;55(7):970-94.
5. [5] Guntay B, Taşınabilir fren dinamiği inceleme cihazı tasarımı ve yazılımı [MSc Thesis]. Ege University, İzmir; 2019.
6. [6] Shridhare, M., Sonar, S., Ranawat, M. and Jindal, A., Estima-tion and reduction of lateral deviation (brake pulling) of a vehi-cle due to difference in left and right wheel brake force, SAE Technical Paper, 2017
7. [7] Tretsiak D, Ivanov V. Investigation on hysteresis losses into disc brake gear for heavy vehicles. SAE paper. 2006 Oct 8:01-3212.
8. [8] Henock A. Design Improvement On The Brake Clearance Adjust-ment Of Sino-Truck (Doctoral dissertation).

9. [9] Tamasho T, Doi K, Hamabe T, Koshimizu N, Suzuki S. Technique for reducing brake drag torque in the non-braking mode. JSAE re-view. 2000 Jan 1;21(1):67-72.
10. [10] Antaaitis DB. Vehicle Level Brake Drag Target Setting for EPA Fuel Economy Certification. SAE International Journal of Passen-ger Cars-Mechanical Systems. 2016 Sep 18;9(2016-01-1925):1157-71.
11. [11] Maintenance Manual no. MM-0350 ELSA 195/225 Reaction Beam Air Disc Brake; 2009.
12. [12] Corminboeuf D. Calibration of bridge standard for strain gauge bridge amplifier. In17th International Congress of Metrology 2015 (p. 04004). EDP Sciences.
13. [13] D’Emilia G, Gaspari A, Iavicoli C, Natale E. Measurement uncer-tainty estimation of gap and profile in the automotive sector. In-Journal of Physics: Conference Series 2020 Jul 1 (Vol. 1589, No. 1, p. 012017). IOP Publishing.