Tire-pressure monitoring system

Tire Pressure Monitoring Systems ( TPMS to, RDK or abbreviated RDC ) or Tire pressure monitoring system ( TPMS) to monitor the tire pressure used in motor vehicles to minimize accidents caused by defective tires, and early on. It can be saved with the optimum tire pressure fuel and avoid unnecessary tire wear. A distinction is made between direct and indirect systems.

Indirect systems

Indirect systems include from the rotational speed of the wheels on a tire pressure or pressure drop. This speed is detected by the vehicle contained in the ABS sensors or sensors for traction control. Indirect systems use pressure monitoring two physical effects:

• Circumference: in the case of a pressure drop in a tire at its outside diameter, whereby the rotational speed of this wheel increases relative to the other is reduced. Thus, it is found when a tire is rotated faster by air loss in comparison to the other three tires. This speed increase is interpreted as pressure drop. The driver is warned. Since this effect is based on the comparison of the wheel speeds with each other, a simultaneous pressure drop in all tires is not detected.
• Frequency effect: the wheels have a characteristic oscillation mode, which can be interpreted as a vibration between the tire and belt wheel. Since this oscillation depends on the pressure at a displacement of the vibration can be closed to a pressure loss. The driver is warned. Since this effect is for each individual wheel, and pressure losses in all four tires at the same time (diffusion) can be recognized here. A position indication of the pressure drop is also possible.

Allen indirect systems have in common that a reset button must be pressed in an adjustment of the air pressure or the installation of new tires. The system then learns the current system behavior as a reference. Learning means that the system, the wheel speeds and frequencies observed during the first phase after reset and the values ​​occurring stores. In the further driving the values ​​occurring with the learned values ​​are compared. When a particular change occurs, the driver is warned. Thus, in the two effects ( rolling circumference, frequency effect ) are considered relative changes - an indication of the pressure is not possible.

Systems based on the use of the rolling circumference, are on the market since 1994. Systems that use both effects, located since 2008 in the introduction.

The legal requirements of ECE R64 and FMVSS 138 will take advantage of the systems, both effects met. Well-known car manufacturers have homologated these systems and upgrade your vehicles as standard so that from.

Indirect systems are typically integrated in the ABS / ESP control unit, isolated solutions also exist in their own controllers. Many automotive suppliers are working to improve the indirect tire pressure monitoring systems, including Continental AG and NIRA Dynamics AB and Sumitomo Rubber Industries and DUNLOP TECH GmbH.

Direct systems

For directly measuring systems, a pressure sensor detects the air pressure and the air temperature of a tire. This information is transmitted along with an identifier of at certain intervals by radio to a control unit in the vehicle. These systems can detect gradual or rapid pressure losses on all tires because they directly monitor the pressure. Depending on the display concept, the driver gets information about the current pressure value in plain text, which he constantly sees in the display either, or can be queried via a button or even a warning of low tire pressure.

For the mounting of the sensors there are currently the following systems:

• In the OEM market: Mounting inside the valve

• Securing to the rim by means of a steel or plastic strip
• Mounting on the valve instead of the valve cap
• Replacing the existing valve against a valve with integrated sensor

For mounting on the valve inside the wireless sensors at the base of specially designed metal valves are screwed; for the tire must be removed; the easiest way is why when mounting new tires. The unbalance (about 40 grams) produced by the sensor weight is compensated by the balancing of the wheel. To provide a pressure monitor or even when the vehicle is an automatic assignment of the module positions, the TPMS modules can be retriggered by a low frequency signal. For this low-frequency antennas are built into the wheel arches. The sensor batteries have a life span of about 7-10 years; then the sensor needs to be replaced because the batteries can not be changed. It is by special batteries that can cover a wide temperature range and not available in retail stores are.

Wherein the fastening means of a band is to be noted that this type of mounting only works reliably when a thinner body is located at the wheel rim and the retaining ribbon is attached expert, since it otherwise of a " slipping " of the sensor or dissolving may tape. This allows the tire to be destroyed within a short time from the inside. For this reason, the concept of attachment by means of belt is rarely used.

Valve Caps wireless sensors are screwed on rubber valves instead of the normal valve caps. They weigh only 10 grams ( including battery), and the battery can be easily replaced. When screwing is to be noted that the sensors may not protrude out from the rim contour; often need to be mounted simply a shorter rubber valve. Again, the wheels should be balanced with the sensors. The valve cap sensors can be easily from summer to winter tires and vice versa change. The advantages of these systems include ease of application. The disadvantage is that at higher speeds the valve is heavily burdened by the occurring centrifugal acceleration. Therefore, these systems are only recommended for slower vehicles. For this retrofit solution, different providers will find on the open market.

For future systems modules are developed by different manufacturers, which are attached directly to the tire. This difficulty can be avoided, which can occur when mounting wheels modules (eg leaks at the valve or destruction during installation ). Furthermore, the possibility arises tire data to be transmitted to the vehicle (eg DOT number or speed index ) with a module position on the tire. With the help of this tire information can be adapted to a control systems such as vehicle dynamics control or anti -lock braking system, on the other hand, the driver is comfortable about his tires. In principle, this tire modules as conventional modules can be powered via batteries with voltage. However, it is also working on μGeneratoren piezo-based, which provide the necessary operating voltage in the tire to operate the modules.

Pros and Cons

The advantages and disadvantages between direct and indirect systems are essentially the costs and functionality. Direct measuring systems need as opposed to indirect systems dedicated hardware in the form of the control unit and sensor modules. Direct systems are therefore more expensive, but they work in more detail. Indirect systems use hardware, which is present within the vehicle such as ABS control units anyway. Only the software is upgraded. This cost advantage continues in operation, since no modules need to be replaced with dead batteries.

Legislation

USA

In the United States (cars, trucks, buses) are required with a gross vehicle weight up to 10,000 lbs ( 4536 kg ) since 2007 tire pressure monitoring systems for all new vehicles. The laws specifying the National Highway Traffic Safety Administration ( NHTSA) FMVSS 138 also describes the exact requirements that must be met by direct and indirect related systems.

EU

In Europe, the European Union launched by the EU Regulation No. 661/2009, a similar legislation. Which entered into force on 19 August 2010 ECE Regulation No 64 shall be equipped with a tire pressure monitoring system since November 1, 2012, all newly homologated vehicles. From 1 November 2014, such a system is then mandatory for all new cars.