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Self-inflating tire technology - rexpress - 08-16-2017 Self-inflating tire technology SIT system description The SIT system is based on highly reliable and proven peristaltic pump principles. It uses the weight and motion of the vehicle to inflate the tire as needed, sourcing air from the outside atmosphere. The whole system consists of only two components a tube chamber functioning as a peristaltic pump for the tire and a pressure management device to control the inflation. The peristaltic tubing is located longitudinally between the rim and the tire wall and copies almost the whole perimeter of the rim. Normal tire deformation caused by the weight of the vehicle creates a closure of the tubing at its lowest point. As the tire moves against the road this closure pushes the air contained inside the tubing into the tire and simultaneously it pulls outside air back into the tubing. As a result, the tire is inflated with the contents of the tubing with each wheel revolution until it reaches its desired pressure. Tests conducted on a regular passenger car wheel have proven that the forces between the deformed tire wall and the rim are sufficient to generate significantly higher pressure than what is needed for tire inflation. SIT peristaltic tubing solution The peristaltic tubing can be implemented into the tire wall in the following way. As there already exists room between a regular tire and rim where the reinforced tire wall is periodically pressed against the rim due to the weight of the vehicle, the tubing can be created as a crevice in the tire side wall. When tire and rim are assembled together, the crevice is sealed by the pressure between them (which is sometimes more than ten times higher than the required tire pressure) and therefore it becomes a sealed tubing inside the tire wall. This could be accomplished by a simple design change in the tire side wall, which, simplified, could be achieved by a modification of the mould in the normal tire production process. The crevice in the tire wall and its sealing during the wheel assembly is shown in figures 3 and 4. It is also possible to create the tubing outside the tire wall as a separate unit placed between the rim and the tire. In that case the tire would just lean on the tubing and enclose it by its deformation, as shown in figure 2. Such a setup was used during the prototype testing. Therefore, SIT can be either a part of the tire or a part of the rim. Upcoming road testing of a pre -production prototype will show which one of the two options will be more suitable for the introduction on the market. SIT pressure management solution The above-described inflation system would pump up the tire with every wheel revolution regardless of whether the tire is under-inflated or not. Therefore a managing system has been designed to turn the inflation ON in case the tire is under-pressured, and turn it OFF once the desired pressure inside the tire has been reached. In case of a properly inflated tire the managing system connects both intake and outlet of the tubing with the inside space of the tire. Therefore the air only circulates between the tubing and the tire with each rotation of the wheel while the pressures remain almost equal. In addition to the intake opening into the tire there is another opening from outside of the tire, equipped with a check valve. This setup of properly inflated tire is shown in figure 5, where the internal air circulation is indicated by the red arrow. When the tire pressure falls below its optimal level the pressure management device closes the intake from the tire and instantly creates a vacuum at the intake part of the tubing. This vacuum opens the check valve and the tube starts pulling air from the outside atmosphere into the tubing and subsequently into the tire. Once the correct tire pressure is reached, the pressure management device again opens the intake of the tubing from the tire, the tubing and tire pressures equalize and the check valve closes down. This setup of under-inflated tire is shown in figure 6, where the stream of inflation air from the outside atmosphere is indicated by the green arrow. In summary, the SIT consists of the tubing with a single opening (1) at its one end leading into the tire and two openings at its other end, one of which (2) leads back into the tire and is equipped with the pressure management device, and the other intake opening (3), equipped with the check valve, leads outside the tire. The pressure management device in its simplest form is a container of compressed air equipped with a membrane. This device is located inside the tire and is therefore surrounded by the air pressure of the tire. The pressure inside this container is pre-set to any desired tire pressure depending on the type of the vehicle the tire is intended for. The membrane is located against the intake opening (3) of the tubing from the tire. As the tire pressure falls below its desired level (the pre-set pressure of the container), the air inside the pressure management device will expand and push the membrane towards the opening (3) and close it. Resulting vacuum in the tubing starts pulling air from the outside atmosphere and the tire gets inflated. Once the tire pressure reaches its optimal level equal to the pressure of the management device, the membrane is drawn out of the opening (3) and the inflation stops. As the pressure management device is always surrounded by the pressure of the tire, there is no big demand on its robustness due to its design, the pressures inside it and outside it will be most of its lifetime equal, and occasionally slightly lower in its surrounding (the inside of the tire) when the tire is under- pressured until it gets properly inflated again. Beside its simplicity, where the whole system consists of only the tubing, check valve and pressure management device, there is another great advantage of this setup. Statistics show, that in order to solve under-inflation caused purely by regular tire leakages, the SIT has to inflate the tire only in every 3000th revolution; or in other words, it would be in operation for 3km out of every 10,000km drive. It means that it would not inflate the tire for the remaining 9,997km. Therefore, most of the time there would be only inside air circulation between the tubing and the tire back and forth with equal pressures between them, which further increases the durability of the system. |