Brakes are very important to human life. As soon as the brake pedal is lifted, they should instantly return to their resting position. If they are not fully recovered, energy losses may occur. The driver is not aware of this and has no influence on how the brake works. However, it can cause a vehicle's carbon footprint to grow.
This phenomenon has been studied by scientists at the Paul Scherrer Institute PSI, as well as staff from ANAXAM and commercial partner Audi Sport. They demonstrated how to visualize and optimize the movement of brake pistons using neutrons from PSI's Swiss Spallation Neutron Resource SINQ to look inside a brake caliper. The rotating brake disc is held in place by the brake caliper in a clamp-like fashion.
When the driver brakes, a series of pistons are pushed forward by hydraulic pressure from the brake line. These pistons compress the two brake pads against the brake disc, causing the disc to stall due to high frictional forces.
Founded by PSI, the technology transfer center ANAXAM in Villigen helps industrial businesses that want to use PSI's research infrastructure. Audi Sport served as the industrial partner of the project. Mathias Kolb, engineer at Audi Sport, was in contact with Matthias Wagner, now senior engineer at ANAXAM. Together with David Mannes of PSI, they developed a technique that allows them to look at the brake caliper in real time and look for ways to optimize it. This is the first time this has been achieved at PSI.
The partners quickly realized that these could not be used because X-rays could not pierce metals. Neutrons are unique in that they are extremely sensitive to light chemical compounds and also nearly transparent to materials such as the metal of the brake caliper. This reveals that the photo clearly shows brake fluid containing hydrogen compounds.
The research, which began in 2021 and ended this year, was made possible by PSI's neutron beamline and expertise. The experiment was carried out on the Neutra beamline of the spallation source SINQ. A detector caught neutrons moving through the system and finally formed a two-dimensional image through the brake caliper.
A brake caliper was mounted in front of the detector by ANAXAM. A specially created hydraulic system has been added to the installation that produces realistic braking pressures of up to 100 bar. The temperature of the brake caliper can be precisely regulated in a climate chamber to simulate various operating scenarios. The brake disc did not bend during tests, unlike on the road.
ANAXAM's Matthias Wagner adds that this "could be a possibility for future testing to reach even more conclusive results." But given that the entire set of measures has already produced a large number of interesting results, it is probably unnecessary.
The images captured by the detector are an astonishing example of the capabilities of neutron imaging.
The brake caliper is easily visible, with six hydraulic pistons, three on each side. The smallest differences in the movement of the pistons are also important.
It is now clear that the lower piston that drives the outer brake pad has 0,4 millimeters of appropriate clearance, but the other five pistons have less than 0,3 millimeters of clearance. The outward bending of the clamp-shaped brake caliper by the pressure of the two brake pads was also precisely measured by the researchers.
This project is a great example of how the skills of ANAXAM and PSI can further develop a product that has already demonstrated its value in mass production.
The industrial partner has improved the performance of the brake pistons to the point where the clearance between the three pistons on the inside of the brake caliper has increased by 0,1 millimeter, as measured under the neutron beam. When the brakes are removed, this successfully separates the brake pads from the brake disc. According to David Mannes of PSI, “Our research can help reduce CO2 emissions from road vehicles.”
📩 31/12/2022 12:51