Abstract


Self
inflating tyre system is an automatic mechanism for maintaining
proper level of pressure inside the vehicle tyres.Or in other words
it is an automatic inflation or deflation system used in tyres.This
system reduces the wear of the tread of the tyre and increases
driving comfort. It also increases fuel efficiency and ensures safe
driving.The main self inflating systems used are CTIS and TMS
systems.


Self-inflating Systems


Tyre-inflation systems have three general goals:
  1. Detect when the air pressure in a particular tyre has dropped – This means they have to constantly (or intermittently) monitor the air pressure in each tyre.
  2. Notify the driver of the problem
  3. Inflate that tyre 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.
  4. Parts of Any Self-inflating System

While the available tyre inflation systems vary in design, they share some common elements.

  • They all use some type of valve to isolate individual tyres to prevent airflow from all tyres when one is being checked or inflated.
  • They have a method for sensing the tyre 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 inboard 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 tyre inflation.
  • There has to be a way to get the air from the air source to the tyres, which is usually through the axle. Systems either use a sealed-hub axle with a hose from the hub to the tyre 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 tyre without risking damage to the hub or rear-axle seals

Central Tyre Inflation System (CTIS)

The idea behind the CTIS is to
provide control over the air pressure in each tyre as a way to
improve performance on different surfaces. For example, lowering the
air pressure in a tyre creates a larger area of contact between the
tyre 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 tyre, maneuverability is greatly
improved.

Another function of the CTIS is
to maintain pressure in the tyres 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.

There are two main manufacturers
of the CTIS: U.S.-based Dana Corporation and France-based Syegon (a
division of GIAT). Dana Corporation has two versions, the CTIS for
military use (developed by PSI) and the Tyre Pressure Control System
(TPCS) for commercial, heavy machinery use. In the next section,
we’ll take a look at the inner workings of a basic CTIS setup.


Here is a look at the overall
system: 
 
Central Tyre Inflation System
Central Tyre Inflation System

A wheel
valve is located at
each wheel end. For dual wheels, the valves are typically connected
only to the outer wheel so the pressure between the two tyres can be
balanced. Part of the wheel valve’s job is to isolate the tyre 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 tyres.

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 tyre 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
tyre-pressure readings to the ECU.

An operator
control panel allows
the driver to select tyre-pressure modes to match current conditions.
This dash-mounted panel displays current tyre pressures, selected
modes and system status. When the driver selects a tyre-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), tyre pressure should
be higher to prevent tyre 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 tyres 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.

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