Future tire information system ITS

Future tire information system ITS

In September 2007, the United States stipulated that all new cars with a load of less than 4.5 tons must be installed with a tire pressure monitoring system. Europe is currently discussing this measure. According to the European Commission ’s opinion, all new models must be equipped with a tire pressure monitoring system from 2012. As one of the world's leading manufacturers of TPMS (tire pressure monitoring system), Continental Group is developing battery-free solutions. ITS (tire intelligent monitoring system) uses piezoelectric technology to convert kinetic energy into electrical energy, thereby replacing battery power. In addition, thanks to the integrated electronics in the tires, ITS can also support a large number of new safety and comfort features.

Introduction

As early as the 1990s, Europe first developed a system for detecting and monitoring tire pressure. Its original purpose is to improve comfort, because the shock absorption characteristics of the tires and chassis adjustment will ultimately have a decisive effect on the car's grip ability and overall comfort. To this end, the conflict of interest between the two major industries of tires and automobiles must be resolved. Tire manufacturers advocate raising tire pressure as much as possible to ensure safety and reduce wear. Automakers insist on moderate tire pressure to achieve higher driving comfort.

In 2000, a series of accidents caused by improper tire pressure in the United States caused great public attention. In response to this situation, in September 2005, the US legislature stipulated that all new cars and light trucks must install a tire pressure monitoring system. In addition to safety, maintaining normal tire pressure also helps reduce carbon dioxide emissions, because insufficient tire pressure will increase rolling resistance and increase fuel consumption. According to estimates. When the tire pressure is lower than 0.5 bar, fuel consumption will increase by 2% to 3%. A 2005 survey conducted by the French road safety agency Securit e RouTI e re shows that if the tire pressure of each car is normal, France alone can reduce carbon dioxide emissions by 1.6 million tons per year. In addition, when the car runs under insufficient tire pressure, it will cause the tire to be replaced in advance.

At present, effective measures are taken to reduce carbon dioxide emissions in favor of environmental protection discussions, making the tire pressure monitoring system once again a hot spot. All cars that use low-pressure safety tires have been forced to install such systems, and a large number of other models can be installed. There are two types of tire pressure monitoring systems: indirect and direct. The two systems are described below.

Indirect detection system

This is the most cost-effective tire pressure monitoring system, which can indirectly detect tire pressure using the signal emitted by the ABS wheel sensor. The system measures the speed of each wheel and calculates the rolling circumference of each tire. Low tire pressure will cause the rolling radius to decrease. When the wheel speed is accelerated, the comparison of the four wheels can detect the possible decrease in tire pressure.

Direct inspection system

Currently, 21 automobile manufacturers have adopted Continental's direct tire pressure monitoring system (above). The tire pressure monitoring system (TPMS) measures the actual pressure in the tire. In addition, the system can simultaneously detect whether the tire pressure of multiple tires has dropped. These systems can be placed in deep grooves inside the hub, or as separate units for tire valves.

The above two systems are composed of batteries and electronic devices, measure the internal pressure of the tire, and transmit the detected value of the tire to the on-board electronic system for inspection and analysis. If necessary, notify the driver of the tire pressure problem.

In order to avoid the false alarm caused by the difference in the heat rate between the wheel and the air in the tire, Continental Group combined with the consideration of this phase shift factor, introduced a special correction factor in the calculation.

The battery provides the maximum space for the improvement of this tire pressure monitoring system. Batteries are large and quite heavy, because to ensure a service life of five to ten years, the volume cannot be made very small. At present, it seems impossible to expect the development of battery technology, there is no room for improvement in this regard. If the battery runs out, the entire tire pressure monitoring electronic unit has to be replaced. For stability reasons, the tire pressure electronic unit uses permanent plastic packaging. To avoid limited service life, Continental is actively developing piezoelectric technology to meet future needs.

ITS: Tire information system using piezoelectric technology

At least in some models, typical mechanical and hydraulic systems have been electronic, such as braking systems and steering systems. In this regard, tires are the only large automotive components that have not yet been touched. In the future, ITS will make tires “smart” to a certain extent, and the system can be integrated with the entire vehicle electronic architecture. Continental Group plans to achieve mass production of ITS in 2010, and is currently discussing cooperation intentions with well-known car manufacturers.

The preliminary functional design of ITS is mainly based on the mature TPMS architecture of Continental, replacing the battery with a piezoelectric converter. Theoretically, the function of the piezoelectric transducer is similar to the well-known piezoelectric fuel injector. In tires, piezoelectric devices convert mechanical motion into electrical energy.

The piezoelectric transducer is composed of spring steel coated with piezoelectric ceramics. As the tire rolls, the piezoelectric ceramic is exposed to tension or pressure. The deformation caused by these two conditions will generate a certain voltage. This voltage is input to the capacitor after rectification. Capacitors are used to configure electronic devices, not specifically for characteristic power supplies. The operation of silicon devices requires a certain amount of voltage, and capacitors can meet this demand. Then. The pressure and tire data are transmitted to the receiver of the car body through the common methods of the TPMS system for analysis by the on-board electronic system.

The main advantage of this method is that in theory there are no restrictions on the function of the wheel electronics. At the same time, the volume and weight of pressure gauges using piezoelectric technology are much lower than battery-powered systems.

At present, the best battery-powered system weighs about 30 grams, and the system using a piezoelectric transformer weighs much less than this number. Since this technology is still in its infancy and still has a lot of room for development, it is expected that its volume will be further reduced in the future.

The advantages of volume reduction are obvious: first, it reduces the bulky volume that has to be rotated and improves portability; second, it reduces the trim weight required for the pressure element. From the perspective of physical principles, the weight of the entire wheel electronics should be less than 10 grams, and the service life must be guaranteed. The battery itself weighs 5 grams, which is difficult to meet this weight goal; on the other hand, the weight of the piezoelectric converter is expected to be further reduced-this is just a problem of further innovation.

Continental Group believes that in theory, ITS is best placed directly in the tire. The main benefits of this are:

· Measure temperature more accurately and quickly without being negatively affected by the wheel hub;

· The module will not be damaged when disassembling the tire;

· No pressure drop due to valve leakage (the valve life is shorter than the battery);

· The contact surface of tire detection is long, the result is more accurate.

If the pressure is still detected at the hub, the piezoelectric transducer is also effective. Even if the position is relatively fixed in this case, the piezoelectric device can still convert the kinetic energy into enough electrical energy to transmit the data to the on-board electronic system.

In addition to the battery, the piezoelectric transducer can also replace another component, the "parking switch". This switch records when the car is driving and reports the movement to the wheel electronic system. When parking, the switch turns off the electronic system, checks the conventional distance, and determines whether the vehicle needs to be moved again. This feature currently significantly extends battery life. Piezoelectric transducers only generate voltage when the car is traveling, so no "parking switch" is needed.

ITS network

Because it is in the center of the inner wall of the tire, ITS can get a lot of information, not just tire pressure. For example, as part of the "functional network" concept, it has been planned to use ITS data to control vehicle power.

In addition to the pressure sensor, the ITS unit also contains two sensors for detecting temperature and acceleration. The information from these sensors can be used to determine tire pressure more accurately, for example, to further reduce false alarms by considering different temperature conditions. This helps to compress the alarm threshold range, which in turn reduces fuel consumption.

In addition, the sensor data can also be used to calculate the tire load capacity. The tire manufacturer's data, such as tire model, can be saved in the electronic system. At the same time, you can also determine the tire condition and mileage.

So, how to generate other tire data? When the tire contact surface appears and disappears, the acceleration can be detected. The acceleration data combined with tire pressure can be used to calculate the tire circumference. Using this information and the length of the contact surface, the force on the tire can be calculated. This force is a measured value of the wheel load, which indicates the load condition of the car when considering four wheels. At the same time, this information can also be used to generate functions to accurately adjust the target tire pressure for load conditions and the center of gravity of the vehicle, thereby saving fuel consumption.

At present, not all tire pressure detection systems can determine the correct target pressure. This means that it is possible for a fully loaded vehicle to continue driving with tire pressure only supporting part of the load. Instead of generating the necessary alarm. ITS eliminates this problem. The vehicle's center of gravity information can be used to improve various safety functions, such as anti-rollover. This function also helps to ensure the safe driving of light trucks and heavy trucks, for example, when the load is shifted during driving.

Taking a medium-sized car with a load of 1.6 tons as an example, each wheel should carry a weight of about 400 kg. Using the voltage generated by the piezoelectric system, it is now possible to determine whether the weight carried by each wheel is indeed 400 kg, or whether such a situation occurs, for example, because the heavy objects are concentrated in the trunk box, causing the rear wheel to be stressed too much. In this case, the electronic system will prompt the driver to adjust the tire pressure to prevent tire damage and avoid additional fuel consumption.

The automatic transmission can also be controlled according to load and power load conditions, for example when the vehicle power and load reach the limit. ITS can provide corresponding information to the transmission control unit, and the control unit transmits the optimal vehicle speed command to the automatic transmission according to the information.

This vehicle load information can also be used to adjust the vehicle's axial and radial forces. This is because the tire parameters cannot be kept constant. Measurable tire conditions such as temperature, load, age, and status can be integrated into vehicle power control systems or used to start safety systems.

ITS can provide information about whether the friction of the road contacted by the wheels is different, so as to better adjust the ABS system. In theory, all the safety functions provided by ITS can be used in commercial vehicles, for example, you need to pay special attention to the safety of dangerous goods transportation vehicles.

In fact, the relationship between sensors and tires is directly established from the beginning of production. This also means that the ITS sensor system can save all relevant data of the tire, such as speed level and tread characteristics. In this way, the vehicle can automatically remind the driver, for example, when it exceeds the maximum speed allowed by the winter tires, it will automatically remind the driver. Moreover, ITS can indicate the wear condition according to the mileage and recommend when to change the tire.

Another advantage of this system is that it is beneficial to low-pressure safety tires. On the one hand, when the tire is leaking, the system can quickly notify the driver; when the tire pressure does drop significantly, the electronic system can automatically monitor the remaining mileage and remind the driver when it is close to the maximum remaining mileage allowed.

At the same time, this system will also enable inter-vehicle communication in the future. For example, tires equipped with a tire information system can collect data on the strength of the grip and notify other vehicles of road attachments, thereby reducing accidents, especially when there is a danger of ice or snow.
In the future, this mechanically sensitive sensor can be used to determine the coefficient of friction. Finally, when determining the rated pressure, the ratio of radial force to axial force is used to determine the friction coefficient. When pressure is applied to the road, the rubber will deform. The piezoelectric transducer inside the tire can detect this movement and convert it into an electrical signal.

Summary and outlook

There is a basic difference between indirect and direct monitoring systems for monitoring tire pressure. Due to the use of batteries as energy sources, the service life of indirect monitoring systems is generally about 10 years.

Continental is currently developing a piezoelectric converter as a power source to replace traditional batteries. Car manufacturers do not need to make major changes, because the use of this device can be integrated with the vehicle system, the remaining system architecture remains the same. In the future, this electronic unit will be installed in the tire. It is no longer installed in the wheel hub or valve like the previous device. Piezoelectric transducers also provide signals that the tire information system will provide new opportunities for chassis tuning and vehicle power control improvements.

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