Concept of a torque sensor for simplex drum brakes
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ORIGINAL PAPER
Concept of a torque sensor for simplex drum brakes Model based sensitivity analyses of an abutment force sensor concept for brake torque determination of simplex drum brakes Christian Vey1 · Hermann Winner1 Received: 3 November 2019 / Accepted: 16 May 2020 © Springer Nature Switzerland AG 2020
Abstract Several studies about the calculation of the brake factor exist, with differences in the degree of detail. One of the best known from Kößler is enlarged in this paper to analyze beside the brake factor the force inside the drum in further detail. Based on this analysis a relation between brake torque and abutment forces is presented, which leads to the idea of an abutment force sensor, to determine the brake torque. To assess this relation a sensitivity analysis is carried out. The results show a low sensitivity against the friction coefficient of the lining. The effects from all other, mainly geometric parameters are discussed to assess the potential of this innovative sensor.
1 Introduction As one of different mega trends in the automotive indus‑ try, electric vehicles (EV) bring a lot of new requirements to the brake system. With the function of recuperation, an additional system is available to achieve the desired decel‑ eration. The high usage of the regenerative braking leads to a reduced energy consumption of the friction brake. This reduced energy consumption increases the risk of corro‑ sion, with an impact to NVH, drag torque and performance [1]. Potential solutions to achieve a higher corrosion resist‑ ance are required. New materials like aluminum discs or coated discs could be a solution, but also known systems with encapsulated design, like drum brakes. Especially drum brakes could be interesting from the point of costs [7]. In today’s vehicles, drum brakes have disappeared from the front axle and are entirely used for the rear axle. This is caused by the lower thermal performance compared with a disc brake and the high sensitivity of the brake factor to changes in the coefficient of friction of the lining. These variations in friction coefficient during operation may result in different brake torques on an axle resulting in an * Christian Vey [email protected]‑darmstadt.de 1
Institute of Automotive Engineering, TU Darmstadt, Otto‑Berndt‑Str. 2, 64287 Darmstadt, Germany
unintentional vehicle movement [2, 8]. Thus, the use of a conventional open loop pressure control for brakes with a high friction sensitivity is not suitable for the requirements regarding stability and comfort. On the rear axle, the inten‑ sity and impact of this effect is significantly lower than on the front axle due to the lower braking force level. This explains the fact that drum brakes are still used on the rear axle of vehicles despite the described problems. To facilitate the use of drum brakes on the front axle in accordance with the performance, driving comfort and stability requirements, developments are necessary. The approach of a closed loop brake torque control shows the potential to reduce or elimin
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