Analysis of the future tire information system ITS tire intelligent detection system

In September 2007, the United States required all new cars with a load capacity of less than 4.5 tons to be equipped with tire pressure monitoring systems. This measure is currently being discussed in Europe, and according to the opinion of the European Commission, all new models must be equipped with tire pressure monitoring systems from 2012. As one of the world's leading manufacturers of TPMS (Tire Pressure Monitoring System), Continental is developing a battery- free solution. ITS (Intelligent Tire Monitoring System) uses piezoelectric technology to convert kinetic energy into electrical energy, thereby replacing battery power. In addition, due to the integration of electronic devices in the tire, ITS can also support a large number of new safety and comfort functions.

Introduction

As early as the 1990s, Europe first developed systems for detecting and monitoring tire pressure. The original purpose was to improve comfort, because the shock absorption characteristics of the tires combined with chassis adjustment will ultimately play a decisive role in the car's grip and overall comfort. To do this, the conflict of interests between the tire and automobile industries must be resolved. Tire manufacturers advocate the highest possible tire pressure to ensure safety and reduce wear. Car manufacturers, on the other hand, 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 attracted great public attention. In response to this situation, in September 2005, the US legislature stipulated that all new cars and light trucks must be equipped with tire pressure monitoring systems. In addition to safety, maintaining normal tire pressure can also help reduce carbon dioxide emissions, because insufficient tire pressure will increase rolling resistance and increase fuel consumption. It is estimated that when the tire pressure is lower than 0.5 bar, fuel consumption will increase by 2% to 3%. A survey conducted by the French highway safety agency Securité Routière in 2005 showed that if the tire pressure of each car was normal, France alone could reduce carbon dioxide emissions by 1.6 million tons per year. In addition, driving a car with insufficient tire pressure will cause the tire to be replaced prematurely.

At present, the discussion on effective ways to reduce carbon dioxide emissions for environmental protection has made tire pressure monitoring systems a hot topic again. All cars with low-pressure safety tires have been required to install such systems, and a large number of other models can be installed as an option. Tire pressure monitoring systems are divided into two types: indirect and direct. The following describes these two systems respectively.

Indirect detection system

This is the most cost-effective tire pressure monitoring system that uses the signals emitted by the ABS wheel sensors to indirectly detect tire pressure. The system measures the rotation speed of each wheel and calculates the rolling circumference of each tire. Low tire pressure will reduce the rolling radius. At higher wheel speeds, a possible drop in tire pressure can be detected by comparing the four wheels.

Direct detection system

Currently, 21 car manufacturers use Continental's direct tire pressure monitoring system (pictured above). Tire pressure monitoring systems (TPMS) measure the actual pressure in the tire. In addition, the system can detect whether the tire pressure drops in multiple tires at the same time. These systems can be placed in a deep groove inside the wheel hub or as a separate unit from the tire valve.

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

To avoid false alarms caused by the difference in thermal rates between the wheel hub and the air inside the tire, Continental has introduced a dedicated correction factor into the calculation, taking this phase shift factor into consideration.

The battery offers the most room for improvement in this tire pressure monitoring system. Batteries are large and quite heavy, and since they cannot be made very small if they are to have a service life of five to ten years, it seems impossible to expect any development in battery technology at present, and there is no room for improvement in this regard. If the battery runs out, the entire tire pressure monitoring electronics unit has to be replaced. For reasons of stability, the tire pressure electronics unit is permanently encapsulated in plastic. To avoid limiting the service life, Continental is actively developing piezo technology for future requirements.

ITS: Tire Information System using piezoelectric technology

At least in some models, typical mechanical and hydraulic systems have been electronicized, such as brakes and steering. In this regard, tires are the only large automotive component that has not yet been touched. Future ITS will make tires "intelligent" to a certain extent, and the system can be integrated with the entire vehicle electronic architecture. Continental plans to achieve mass production of ITS in 2010 and is currently discussing cooperation intentions with well-known automobile manufacturers.

The initial functional design of ITS is mainly based on Continental's mature TPMS architecture, replacing the battery with a piezoelectric converter . In theory, the function of a piezoelectric converter is similar to the well-known piezoelectric injector. In the tire, the piezoelectric device converts mechanical motion into electrical energy.

The piezoelectric converter consists of spring steel coated with piezoelectric ceramic. When the tire rolls, the piezoelectric ceramic is exposed to tension or pressure. The deformation caused by these two situations generates a certain voltage. This voltage is rectified and input into the capacitor. The capacitor is used to configure electronic devices, rather than being used specifically for characteristic power supplies. Silicon chip devices require a certain amount of voltage to work, and capacitors can meet this need. Subsequently. The pressure and tire data are transmitted to the receiver on the car body through the common methods of TPMS systems for analysis by the on-board electronic system.

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The main advantage of this approach is that in theory there are no restrictions on the functionality of the wheel electronics. At the same time, the size and weight of a pressure gauge using piezoelectric technology are significantly lower than a battery-powered system.

Currently, the best battery-powered systems weigh about 30 grams, while systems using piezoelectric transducers weigh much less than this figure. Since this technology is still in its infancy, there is still a lot of room for development, so the size is expected to be further reduced in the future.

The advantages of reduced size are obvious: first, less bulky volume that must be rotated, which increases lightness; second, less balancing weight is required for the pressure element. From the perspective of physics, the weight of the entire wheel electronics should be less than 10 grams, but the service life must be guaranteed. The battery itself weighs 5 grams, which makes it difficult to meet this weight target; on the other hand, the weight of the piezoelectric converter is expected to be further reduced - it is just a matter of further innovation.

Continental believes that, in theory, it is best to place the ITS directly in the tire. The main benefits of doing so are:

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

The module will not be damaged when removing or installing the tire;

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

The tire testing contact surface is long, and the results are more accurate.

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

In addition to the battery, the piezoelectric converter can also replace another component, the "parking switch". This switch registers when the car is moving and reports the movement to the wheel electronics. When parking, the switch switches off the electronics, checks the normal distance between vehicles and determines whether the vehicle needs to be moved again. This function currently significantly extends the service life of the battery. The piezoelectric converter only generates voltage when the car is moving, so there is no need for a "parking switch".

ITS Network

Due to its central location on the inner wall of the tire, the ITS can obtain a lot of information, not just the tire pressure. For example, as part of the "functional network" concept, it is planned to use ITS data to control the vehicle dynamics.

In addition to the pressure sensor , the ITS unit also contains two sensors for temperature and acceleration. The information from these sensors can be used to determine the tire pressure more accurately, for example, by taking different temperature conditions into account to further reduce false alarms. This helps to shorten the warning threshold range and thus reduce fuel consumption.

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

So how do you generate other tire data? Acceleration can be detected as the tire contact patch appears and disappears. Acceleration data combined with tire pressure can be used to calculate the tire circumference. Using this information and the length of the contact patch, the tire force can be calculated. This force is a measure of the wheel load and indicates the vehicle loading condition when considering all four wheels. At the same time, this information can be used to generate a function to accurately adjust the tire target pressure for the loading condition and the vehicle's center of gravity, thereby saving fuel consumption.

Not all tire pressure monitoring systems currently determine the correct target pressure. This means that a fully loaded vehicle can be driven with tire pressure that only supports part of the load. The necessary warning is not generated. ITS eliminates this problem. The vehicle's center of gravity information can be used to improve various safety functions, such as rollover prevention. This function also helps to ensure the safe driving of light and heavy trucks, for example, when the load shifts during driving.

Taking a mid-size 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 the situation is such that, for example, the weight is concentrated in the luggage box, causing excessive forces on the rear wheels. In this case, the electronic system prompts 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. The ITS can provide corresponding information to the transmission control unit, which transmits the optimal vehicle speed command to the automatic transmission based on the information.

This vehicle load information can also be used to adjust the axial and radial forces of the vehicle. This is because tire parameters cannot remain constant. Measurable tire conditions such as temperature, load, age and condition can be integrated into the vehicle dynamics control system or used to activate safety systems.

ITS can provide information about whether the friction of the road surface in contact with the wheels is different, so that the ABS system can be better adjusted. In theory, all the safety functions provided by ITS can be used in commercial vehicles. For example, special attention should be paid to the safety of vehicles transporting dangerous goods.

In fact, the relationship between sensor and tire is established directly from the beginning of production. This also means that the ITS sensor system can save all relevant data about 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 for winter tires. And ITS can indicate wear based on mileage and recommend when to replace the tires.

Another advantage of this system is that it is beneficial to low-pressure tires. On the one hand, the system can quickly notify the driver when the tire is leaking; and 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, a tire equipped with a Tire Information System
can collect data on the strength of its grip and inform other vehicles about the road adhesion, thus reducing accidents, especially when there is a risk of ice and snow. In the further future, this mechanically very sensitive sensor can be used to determine the coefficient of friction. Ultimately, when determining the rated pressure, the ratio of radial force to axial force determines the coefficient of friction. When pressure is applied to the road surface, the rubber deforms. A piezoelectric converter inside the tire detects this movement and converts it into an electrical signal.

Summary and Outlook

There is a basic difference between the indirect and direct monitoring systems for monitoring tire pressure. Since batteries are used as energy, the service life of indirect monitoring systems is generally about 10 years.

Continental is currently developing piezoelectric converters as a power source to replace conventional batteries. Car manufacturers do not need to make major changes, because with this device, which can be integrated with the vehicle system, the rest of the system architecture remains the same. In the future, this electronic unit will be installed in the tire. Instead of being installed in the wheel hub or on the valve as in the past. The signal provided by the piezoelectric converter also means that the tire information system will provide new opportunities for chassis adjustment and improved vehicle dynamics control.