PRESSURE CONTROL IN ISOLATED TIRES USING
SELF- INFLATING SYSTEM
Department Of Automobile Engineering
PSG College of Technology
M.PRASAD V.THANAJAYAN R.THIYAGARAJAN
PSG College of Technology PSG College of Technology PSG College of Technology
Coimbatore Coimbatore Coimbatore
Abstract:
This paper talks mostly about the tires, which form the simplest component of the Automotives to
a novice, but for an experienced person it’s undoubtedly the most critical component on a
vehicle. 80% of the tires on roads are under-inflated and they cause a significant reduction to the
performance, safety conditions and of course the economy of the usage. The above-specified
problems could be overcome by incorporating Self-Inflating Tire System into the automotives.
The basic functions of this system like Detection, Notification and Inflation are clearly enunciated
in the paper. The main emphasis is on how the isolated tire is being inflated without jeopardizing
the existing onboard air supply by using the necessary components at essential places. The
systems of various types depending on the application and the mechanisms involved are
accounted.
Keywords: Tires- Problems faced- Pressure Control
Introduction:
Tires are undoubtedly the most critical safety component on a vehicle. Where the rubber meets
the road affects traction, handling, steering, stability and braking.
Lot of interest is being shown in this subject because numerous innovative ideas could be
implemented. Earlier, only the vehicles belonging to the high strata used this system but now this
system is widely used for its manifold advantage to the vehicles. Some of the advanced features
that are being added to improvise the system for convenient usage are:
Convenient push button operation, which allows accurate selection of tire pressure.
Automatic over-speed protection, which inflates tires to the required pressure for vehicle
speed.
Tire maintenance feature checks and maintains pressure at selectable time intervals.
Multi-channel pressure control available by axle groups.
Reasons for Failure of tires:
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There are many reasons why tires fail:
FAILURES CAUSED BY UNDERINFLATION
FAILURES CAUSED BY OVERINFLATION
FAILURES CAUSED BY OVERLOADING
FAILURES CAUSED BY IMPACT/ROAD HAZARDS
FAILURES CAUSED BY STRUCTURAL DEFECTS
FAILURES CAUSED BY EXCESSIVE SPEED
FAILURES CAUSED BY INSTALLATION ERRORS
About 80% of the tires on the road are under-inflated. This is caused because of frequent impact
with potholes and sometimes because of environmental conditions. There is loss of at least 2 psi
of air during summer or winter. The following picture shows the outline of the tires in different
conditions and the worn-out areas are indicated below them.
All the above said problems could be overcome by a self-inflating tire which could automatically
adjust the tire pressure according to the kind of terrain. This system would enhance the
performance and safety conditions to the vehicle.
Self-Inflating systems
Basic inflating system should have the following operations:
Detection: The pressure in the tires is constantly monitored.
Notification: The driver is notified about the changes.
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Inflation: The tires are inflated to the proper level and see that the valve is opened
only when it is needed.
Parts of Any Self-Inflating System:
SITS all use some type of valve to isolate individual tires to prevent airflow from all tires when
one is being checked or inflated.
They have a method for sensing the tire pressures. This is addressed in most cases with central
sensors that relay information to an electronic control unit and then to the driver. They have an
air source, which is usually an existing onboard source such as braking or pneumatic systems.
When using an existing system, however, they have to ensure that they don't jeopardize its
original function. For this reason, there are safety checks to ensure that there is enough air
pressure for the source's primary use before pulling air for tire inflation.
There has to be a way to 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.
There has to be a pressure relief vent to vent air from the tire without risking damage to the hub
or rear-axle seals.
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. For example, lowering the air pressure in a tire
creates a larger area of contact between the tire and the ground and makes driving on softer
ground much easier. It also does less damage to the surface. This is important on work sites and
in agricultural fields. By giving the driver direct control over the air pressure in each tire,
maneuverability is greatly improved.
Another function of the CTIS is to maintain pressure in the tires if there is a slow leak or
puncture. In this case, the system controls inflation automatically based on the selected pressure
the driver has set.
CITS OUTLOOK:
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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.
An electronic control unit (ECU) mounted behind the passenger seat is the brain of the system. It
processes driver commands, monitors all signals throughout the system and tells the system to
check tire pressures every 10 minutes to make sure the selected pressure is being maintained.
The ECU sends commands to the pneumatic control unit, which directly controls the wheel
valves and air system. The pneumatic control unit also contains a sensor that transmits tire-
pressure readings to the ECU.
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.
When vehicles are moving faster (like on a highway), tire pressure should be higher to prevent
tire damage. 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 time,
the system automatically inflates the tires to an appropriate pressure for that speed. 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.
A Closer Look:
The electronic control unit tells the pneumatic control unit to check current pressure and either
inflate or deflate the tire to the pressure selected by the driver. If the system determines that
inflation is needed, it first checks to make sure that brake pressure reserves are where they
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should be; 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.
In this illustration, you can see the pathway that the air travels for inflation or deflation once it
gets to the wheel. The tubing runs from the vehicle's air compressor through the wheel hub and
then to the tire valve. The "quick disconnect fitting" allows the tire to be separated from the CTIS
system for removal or servicing.
This diagram also shows the Hummer's run-flat feature, which allows the tire to continue
supporting the vehicle even when it will not hold any air.
Tire Maintenance System (TMS):
Tire Maintenance System is a "smart" system for tractor trailers that monitors tire pressure and
inflates tires as necessary to keep pressure at the right level. It uses air from the trailer's brake
supply tank to inflate the tires.
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The system has three main components:
The tire hose assembly provides the air route to inflate the tire and has check valves so that the
air lines and seals do not have to be pressurized when the system is not checking or inflating the
tires. This cuts down on wear and tear on the seals.
The rotary joint is comprised of air and oil seals and bearings and connects the air hose from the
non-rotating axle to the rotating hubcap. Its air seals prevent leakage, and the oil seal prevents
contamination. The rotary hub also has a vent to release air pressure in the hubcap. The
manifold houses the pressure protection valve, which makes sure the system doesn't pull air if
the brakes' air supply is below 80 psi. It also houses an inlet filter to keep the air clean, a
pressure sensor to measure tire pressures and solenoids that control airflow to the tires.
Like the CTIS, this system also has an electronic control unit that runs the entire system. It
performs checks to make sure the system is operational, notifies the driver via a warning light on
the trailer (visible through the rear-view mirror) if a tire's pressure drops more than 10 percent
below its normal pressure and performs system diagnostics.
The system performs an initial pressure check and adds air to any tire that needs it. The check
valves in each tire hose ensure that the other tires don't lose pressure while one tire is being
inflated. After an initial pressure check, the system depressurizes to relieve pressure from the
seals. Every 10 minutes, the system pressurizes the lines and rechecks tire pressures.
The system measures tire pressure using a series of air pulses in the air lines. If the target
pressure in the line is not reached after a certain amount of time, the system begins inflating the
tire(s) until the correct pressure is reached.
AIRGO System:
The AIRGO system is a
constant monitoring
system that uses a series of
check valves to detect a loss in
air pressure.
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Unlike some of the other systems, AIRGO doesn't use air from the vehicle's braking system.
When air seepage has occurred at any of various points in the system
(1), the system draws air
(2) from the vehicle's pneumatic system (not shown) and sends it by way of the vehicle's axles
(3) through the hubcap assembly (4) and into the tire requiring inflation.
A warning light, located on the trailer but visible through the driver's rearview mirror, illuminates
when the system has inflated a tire.
Since this is a constant monitoring system, which puts a lot of wear and tear on the seals,
AIRGO uses carbon-graphite and case-hardened steel for its seals rather than rubber.
Meritor Tire Inflation System (MTIS)
The MTIS is designed for use on tractor trailers. It uses compressed air from the trailer to inflate
any tire that falls below its appropriate pressure. Air from the existing trailer air supply is routed to
a control box and then into each axle.
The air lines run through the axles to carry air through a rotary union assembly at the spindle end
in order to distribute air to each tire. If there is significant air-pressure loss, an indicator light
informs the driver.
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The overall system is made up of a wheel-end assembly and a control module.
Wheel-end assembly:
The wheel-end assembly includes a flexible hose with check valves. The check valves only allow
air to flow into each tire; this ensures that while one tire is being inflated, the other tires don't lose
air pressure.
This assembly also
incorporates a
stator (a non-rotating part) inside the axle spindle and a flow-through tee that is attached to the
hubcap. The flow-through tee has a dynamic seal to allow rotation while preventing pressure loss
when pressurized air passes from the axle to the hub, which occurs through a tube that runs
from the stator into the tee.
In the hubcap assembly, there is a vent to make sure pressure does not build up in the wheel
end. A deflector shield keeps contaminants such as dirt and water from entering the wheel end.
For axles with hollow spindles, a press plug seals the pressurized axle interior from the wheel
end in order to secure the stator.
System Controls:
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. Like some of the other systems that use onboard air supplies,
this system has a pressure protection valve so that it won't pull air if the air supply is below 80
psi.
A system pressure adjustment knob allows for adjustments to the overall system air pressure. A
flow-sensing switch activates the indicator light to let the driver knows if a significant amount of
air is being pumped into a tire, which would indicate a potential puncture.
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Conclusion:
As most drivers have no time to constantly vigil over the pressure conditions of the tires, this
simple solution realized in elegant design is the complete solution. And this concept could be
incorporated in manifold designs making it an interesting topic for the budding engineers to work
on. This paper has served its purpose in clearly defining the Self-inflating tire system and
enunciating the working part with easy-to-understand pictorial views. And the obvious task that
would follow this would be able to design an innovative concept with more interesting features.
