1. Presented by : AJEESH.G S7 ME Class no.4429

2. Introduction Self-inflating tires allow a vehicle to adjust to the current terrain for ideal performance and safety in those conditions. Self-inflating tires are designed to constantly maintain tire pressure at the proper level. Self-inflating systems are designed more for slow leaks and for optimizing performance and safety Self-inflation systems helps in re-inflation of tires to proper level

3. Tire-Inflation Basics On roads 80 percent of the cars are driving with one or more tires under inflated. Tires lose air through normal driving and seasonal changes in temperature They can lose one or two psi (pounds per square inch) each month Under inflation is bad for tires. Affect gas mileage. Generally unsafe.

4. Tire-Inflation Basics When tires are under inflated, the tread wears more quickly 15 percent fewer miles you can drive on them for every 20 percent that they're under inflated. Under inflated tires also overheat more quickly than properly inflated tires

5. How tires support a car There is a flat spot on the bottom where the tire meets the road. this flat spot is called contact patch When the tire is spinning,the contact patch must move around the tire to stay in contact with the road At the spot where the tire meets the road the rubber is bent out. it takes force to bend that tire and the more it has to bend the more force it takes. The tire is not perfectly elastic, so when it returns to its original shape it does not return all of the force that it took to bend it. Some of that force is converted to heat in the tire by the friction.

6. Continued………  Since an under inflated or overloaded tire needs to bend more,it takes more force to push it down the road,so it generates more heat.  Tire manufacturers publishes a coefficent of rolling friction for their tires.  We can use this number to calculate how much force it takes to push a tire down the road.

7. CRF for various tires Tire TypeCoefficient of Rolling Friction Low rolling resistance car tire 0.006 - 0.01 Ordinary car tire0.015 Truck tire0.006 - 0.01 Train wheel0.001

8. Continued…. Force required to overcome the friction=crf x weight on the tire. Thus we can provide proper inflation by knowing crf,speed with which we drive, weight of the tire

9. Tire-Inflation Basics The faded areas below indicate areas of excessive tread wear

10. How Tires Fails? Tires flatten at the bottom when they roll. Rebounds to its original shape once it is no longer in contact with the ground. Creates a wave of motion along with some friction. Under inflated tires, waves are larger and the friction created is greater Friction creates heat. If enough heat is generated, the rubber that holds the tire's cords together begin to melt And the tire fails

11. Disadvantages of improper inflation Hence the friction created is greater. Friction creates heat and if enough heat is generated the rubber that holds the tire cords melts and tire trails. Because of the extra resistance an under inflated tire has when it rolls,the cars engine has to work harder. As it effects mileage it can cause severe loss in the cost considerations.

12. Self-inflating Systems Tire-inflation systems general goals: Detect when the air pressure in a particular tire has dropped - This means they have to constantly (or intermittently) monitor the air pressure in each tire. Notify the driver of the problem Inflate that tire back to the proper level - This means there has to be an air supply as well as a check valve that opens only when needed.

13. Self-inflating Systems Parts of A Self-inflating System Valve to isolate individual tires Central sensors for sensing the tire pressures.these Air source, which is usually an existing onboard source Get the air from the air source to the tires, which is usually through the axle Systems either use a sealed-hub axle with a hose from the hub to the tire valve or else they run tubes through the axle with the axle acting as a conduit. A pressure relief vent to vent air from the tire without risking damage to the hub or rear-axle seals.

14. Central Tire Inflation System (CTIS) The idea behind the CTIS is to provide control over the air pressure in each tire As a way to improve performance on different surfaces. Driver can give direct control over the air pressure in each tire To maintain pressure in the tires if there is a slow leak or puncture. System controls inflation automatically based on the selected pressure the driver has set.

15. CTIS: Inside Parts are: A wheel valve Electronic control unit Pneumatic control unit Operator control panel Speed sensor Pressure switch

16. wheel valve A wheel valve is located at each wheel end. Part of the wheel valve's job is to isolate the tire from the system when it's not in use in order to let the pressure off of the seal and extend its life. The wheel valve also enables on-demand inflation and deflation of the tires.

17. operator control panel An operator control panel allows the driver to select tire- pressure modes to match current conditions. This dash-mounted panel displays current tire pressures, selected modes and system status. When the driver selects a tire-pressure setting, signals from the control panel travel to the electronic control unit to the pneumatic control unit to the wheel valves.

18. Speed sensor  The ctis includes a speed sensor that sends vehicle speed information to the electronic control unit.  If the vehicle continues moving at a higher speed for a set period of times, the system automatically inflates the tires to an appropriate pressure for that speed.

19. Pressure Switch This type of system uses air from the same compressor that supplies air to the brakes. A pressure switch makes sure the brake system gets priority, preventing the CTIS from taking air from the supply tank until the brake system is fully charged.

20. A Closer Look

21. How it Works? The electronic control unit tells the pneumatic control unit to check current pressure If the system determines that inflation is needed, checks brake pressure If they are, it applies a slight pressure to the wheel valve to allow inflation. If the tires are over inflated, the system applies a slight vacuum to the wheel valve. When the pneumatic control unit reads that the appropriate pressure is reached, The valve closes.

22. Wheel end assembly  The wheel end assembly includes a flexible hose with check valves.  The flow through tee has a dynamic seal to allow rotation while preventing pressure loss when pressurized air passes from axle to the hub  This occurs through a tube thjat runs from stator into the tee.  In the hub cap aaembly there is a vent to make sure pressure does not build up in the wheel end.

23. Control system  The system control module has a shut-off valve to stop air from being sent to the system, as well as a filter to remove moisture and contaminants. The petcock releases system pressure so maintenance can be performed.

24. Pressure gauges  When the pressure guage is applied to the valve stem of a tire the pressurised air from the tire rushes in and pushes the piston towards the right.  The distance the piston travels is relative to the pressure in the tire.  To allow you to read the pressure there is a calibrated rod inside the tube.

25. Tyre Maintanence Sytem (TMS SYSTEM)  A warning light located on the trailer but visible through drivers rearview mirror,illuminates when the system has inflated a tire.

26. Future of self inflating tyres one of the major systems in the developmental stages is the entire system. This system uses a valve that pulls in air from the atmosphere.it then pumps the air into the underinflated tire using a peristaltic pump action. The goal is to maintain a specific pressure.

27. Conclusion Thus self inflating tires help us to attain certain helpful criterions such as I providing safe driving improve fuel efficiency To control tire pressure according to driving conditions

28. REFERNCES *Crouse Anglin,”Automotive Mechanics”,Tata McGraw Hills *www.howstuffworks.com *www.cycloid.com *www.goodyeartyres.com