Tyre pressure monitoring system, commonly abbreviates as TPMS is an electronic system designed to monitor the air pressure inside a pneumatic tyres on various types of vehicles, and display the data to the driver in real-time over either a gauge, a pictogram display, or a simple low-pressure warning light.
TPMS are designed into the following two basic types: -
- Direct Systems (dTPMS).
- Indirect Systems (iTPMS).
Direct Systems (dTPMS)
In this system, a sensor is installed in each tyre. The sensor measures the tyre's inflation pressure and at times, with advanced sensors, as well as the air temperature in the tyre. The sensors send their current measurement values at regular intervals to the vehicle's control unit. In this way small deviations can be individually identified for each tyre and immediately displayed to the driver. The sensor battery have different lifetimes. A vehicle fitted with a direct tyre pressure monitoring system can only be run on wheels fitted with TPMS sensors.
Indirect Systems (iTPMS)
Using the ABS sensors installed in the vehicle, it is possible to calculate the tyre inflation pressure from the wheel RPM and the tyre rolling circumference. If the tyre pressure (and therefore the rolling circumference) changes, this indicates a loss of pressure. Fundamental to this principle is the calibration of the system with exactly the right tyre pressure.
In the indirect system, two effects are assessed. Firstly, the tyre rolling circumference: If there is a loss of pressure, the rolling circumference becomes smaller and the wheel must rotate more quickly compared to the other wheels. This change is noted and the driver is warned. Secondly, the frequency of oscillation between the tyre and the rim is examined: When this drifts, it can be interpreted as a loss of pressure. In general, the following applies: Indirect systems must be re-calibrated each time a tyre is fitted or the tyre inflation pressure is changed.
*TPMS low pressure warning icon
Advantages of TPMS
The dynamic behavior of a pneumatic tyre is closely connected to its inflation pressure. Key factors like braking distance and lateral stability require the inflation pressures to be adjusted and kept as specified by the vehicle manufacturer. Below are some of the key advantages of TPMS:-
- Improved safety: Avoiding traffic accidents.
- Fuel savings: Early warning of low pressure that could cause high rolling resistance that results in extra fuel use.
- Extended tyre life: Early recognition of a hazardous state of the tyres.
- Decreased downtime and maintenance: Eliminates the hassle of checking the tire pressure with a manual gauge.
- Reduced risk of hydroplaning.
- Environmental efficiency: Under-inflated tyres, as estimated by the Department of Transportation, release over 26 billion kilograms (57.5 billion pounds) of unnecessary carbon-monoxide pollutants into the atmosphere each year in the United States alone.
History of TPMS
- TPMS is mandatory when using run-flat tyres.