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29/08/2014
TIRES AND PRESSURE

TPMS

 


Pneurama inaugurates a series of articles dedicated to the tire pressure monitoring system. We start in this issue with a regulatory and technical analysis


Donaldo Labò

 

 


Foreword     

                                                                                  

Tires and pressure have always been an inseparable duo by definition. To function correctly, performing those basic tasks needed for a vehicle’s motion, this “elastic casing” must be maintained at the exact pressure set by the vehicle’s manufacturer for different conditions such as load, speed, handling, etc.

As widely accepted, the chemical / physical properties of the materials used and the technology of related components (rubber, rim, valve stem) cannot possibly guarantee the perfect tightness of the original pressure, supplied during assembly, over time. Setbacks and problems during the normal use of a vehicle, makes regular checkups necessary on the part of the vehicle’s owner.

Considering the report by the European Manufacturers Technical Board (ETRTO) the advice is: << due to natural permeability, changing weather patterns, damages inflicted to wheels and valve stem, regular pressure control, including spare tires, should be performed every fifteen days>>.

In reality, all too often drivers, if we are to believe the results conducted in a number of countries over the last few decades, forget to perform this task, though important for road safety, for reducing fuel consumption and exhaust emissions. Based on this topic, Federpneus launched a campaign in our country in the year 2000, aimed at raising awareness, through the website “Pneumatici sottocontrollo” (tires under control).

 

 

The legislative framework


The substantial influence that tire pressure has over the efficiency of a vehicle forced some European manufacturers, starting back in the 80’s and throughout the 90’s, to consider applying pressure control systems on some of their high-range models (Porsche, Peugeot, Renault).

The system was introduced in the United States of America back in 1997 by General Motors on the fifth generation Corvettes, along with the first run-flat tires, but it was only after a series of accidents that it was adopted in the TREADAct legislation, whose mandate anticipated the use of control systems on motor vehicle to warn the driver against tire under-inflation.

Throughout the E.U. the adoption of tire pressure control systems was ratified – for new approvals from November 2012, and for all new vehicles sold starting from November 2014 – by the Regulation n°661 dated 2009 on Safety and thereafter introduced also in the UNECE Regulation No. 64, establishing the approval requirements on temporary-use spare tires.

TPMS are now mandatory, since January 2014, on motor vehicles and light vehicles also in South Korea, and Japan as well as other countries will follow shortly.

It should be noticed, however, that the recent introduction of run-flat tires as original equipment has already entailed the need to equip vehicles with control systems, so as to warn the driver against a current loss of pressure, otherwise difficult to detect due to the characteristics of such tires, able to run flat for a limited distance and at a limited speed (i.e. 80 km, at a speed not higher than 80 km/h).

A few aspects touched by these regulations:  

 

(CE) REGULATION N. 661/2009 OF THE EUROPEAN PARLIAMENT AND THE COUNCIL of July 13, 2009 on motor vehicle general safety approval requirements, including their trailers, systems, components and any technical feature.

 

To begin with we must point out that “ it would be opportune to set requirements pertaining to the general safety of motor vehicles and environment efficiency of tires, since current tire pressure control systems increase both safety and environmental efficiency “.

It is later stated (Art.3 c.7) << tire pressure control system: a device assembled on a vehicle able to read the tire pressure or the variation of the pressure over time and pass the information on to the driver while in motion>>. The above mentioned alternative has allowed to develop systems (direct) able to read the pressure through a sensor built in the tire, or (indirect) able to detect the different tire pressure among the different wheels controlling the rotational speed of each wheel.

Art.9 specifies that the vehicles involved belong to the so called M1 category, that is, small passenger transport vehicles, maximum 8 seats excluding the driver, and a GVW of 3,5t, and that the tire pressure control systems must produce, if needed, a warning signal inside the vehicle for the driver, in case a loss of pressure in one of the tires is detected, in order to optimize fuel consumption and road safety. To achieve all this, certain limits have been included in the technical specifications…..etc.

 

ECE REGULATION - R64 (United Nations Economic Commission for Europe)


It is related to the approval of vehicles in the M1 class (up to 3,5t GVW) and N1 (with fixed axles), specifying the rules when these are equipped with:

-limited use spare tires (also called “donut” tires)

-run-flat tires and relative systems

-tire pressure control systems        

Vehicles equipped with self-supporting tires (SST) must, in fact, already possess a control/warning system when running flat to ensure the correct mode of operation between 40 km/h and the vehicle’s top speed.

An alternative principle defining the tire pressure control system states <<……capable of developing a constant evaluation of the tire pressure, or the relative variation of it over a period of time, and passing the corresponding information on to the driver while travelling>>.

The system’s testing provide for, among other things:

-the correct mode of operation between 40 km/h and the vehicle’s top speed;

-measuring the pressure loss following an accidental event (puncture test);

-the activation of a warning signal at the latest 10 minutes after the tire pressure has decreased by 20% in at least one tire, or has reached the limit of 150 kPa (the system detects automatically the most critical between the two);

- warning signal failure test: within 10 minutes of a warning signal failure, another signal must warn the driver of the lack of information received due to failure of the warning system. If the problem is due to radio-electric interference, it may take a little more than 10 minutes.

Arrangement of approval mark for a vehicle equipped with a tire pressure control system, as determined by regulation 64:



Direct TPMS


Sensors, placed inside each tire (and connected to the valve), read the real tire pressure, taking into account the temperature, and communicate immediately via the ECU (electronic control unit) through a radio wave (434 MHz). The receiver processes the data and thereafter sends to a display the pressure value of each tire, as every sensor is fitted and set to read the pressure of each tire.

The data collection is precise, and informs the driver on the condition of each tire even when the vehicle is standing still.


Indirect TPMS


The system does not measure the actual tire pressure, but through the ABS (o ESP) sensors reads the different rotational speed of each wheel. As a tire loses pressure, the rolling radius also changes, and therefore, the rotational speed of the tire, at the same speed. The system reads the irregularity and sends it to the display for the benefit of the driver (to be discussed in future issues).

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