# Brake Torque Sensor Calibration Device
## 1 Introduction  
More than 130 years have passed since the world's first car with a gasoline engine was produced. Whether it was a car of the distant past or the cars of today, they all need to stop at the right time and in the right place, which requires brakes. Constantly increasing demands for ecological and environmental sustainability have increased the demands for the operation of cars and, ultimately, for the brakes themselves. The current trend is to reduce fuel consumption as much as possible, influence the amount of emissions from the combustion of hydrocarbon fuels, and reduce the particle of matter emissions from the wear of brake friction materials and vehicle tires. As stated [1], particulate matter (PM) is one of the world's most problematic pollutants in terms of harm to the environment and human health. Brake dust emissions represent on average 21% of PM emissions in the air, while their share increases near the edges of roads and at intersections, or other places where it is necessary to adjust the traffic speed [2; 3; 4; 5; 6]. The statistics show that motor vehicle exhaust emissions have a decreasing trend, while the amount of non-exhaust emissions gradually increases [7; 8; 9; 10]. Several tests demonstrated that PM emissions significantly increased at the brake temperature of 130 \({}^{\circ}\)C and higher during long-term or intensive braking [11]. With the increasing dimensions of cars, the increasing weight of vehicles, and the increasing payloads of vehicles, there is a higher production of PM emissions. The amount of these emissions also affects the technical condition of vehicles, or their braking systems [12]. A lot of research work has been conducted on the production and distribution of brake particulate matter [13]. Based on PM size distribution from brakewear, 84% of total PM emissions are considered as PM1, i.e., smaller than 1 \(\upmu\)m [1; 14]. [PERSON] et al. [15] report that minimal knowledge about the morphology, chemical composition, and toxicity of nano- and micro-sized particles released from automotive brakes is alarming due to the fact that brake manufacturers are currently not required to develop eco-friendly formulations, particularly when over 70% of the U.S. and only a slightly smaller amount of European brake linings are being imported, which makes it more difficult to control all aspects of these imported brake linings. The authors of refs. [16; 17] pointed out that the different kinds of friction materials, LM, SM, and NAO, behave differently considering the differences that can be observed in the friction layer's morphology, resulting from the different wear mechanisms. Apart from PM, squeal is another harmful effect of the operation of a brake system. Squeal is generated due to the contact of the friction couple during braking and with the related high frequency of the vibration of the brake system components [18]. However, there are many cases, in which the residual torque after braking leads to unpleasant noise, which is given off during vehicle movement [19; 20]. This residual torque not only causes squeals but also negatively contributes to the drag [21; 22; 23]. Based on the facts described above, there are efforts to minimize the residual torque of the brake system of vehicles. The issue is to determine the value of this residual torque. It is possible to find it experimentally by means of a suitable calibration device [24; 25]. In all cases, a strict relationship exists between the composition of the friction layer forming on the mating surfaces and the composition of the emitted particles. The residual torque of the brake plays a significant role in this issue. This is the torque that is created by the contact of the brake element with the disc after the brake is released. For the measurement results of this torque to be as accurate as possible, it is necessary to ensure the high accuracy of the entire measuring device, especially the torque sensor.