Research on Micro-vibration Generator for Powering Tire Pressure Alarm System

Wenjing ZHANG,Haitao YAN,Ximing ZHENG,Zhen YAN,Dongping WANG

1.Modern Institute of Technology,Hebei Agricultural University,Baoding 071000,China;

2.College of Information Sciences and Technology,Hebei Agricultural University,Baoding 071000,China

3.Mechanic & Electronic College,Hebei Agricultural University,Baoding 071000,China

Responsible editor:Tingting XU Responsible proofreader:Xiaoyan WU

In order to improve the safety,extend the life of tires and avoid the occurrence of accidents caused by flat tires,we have therefore researched and developed a sensor to detect the leaks of tires by using the power-generation devices of the piezoelectric power generation device and the energy store.

This device can also be used in agricultural machineries and vehicles.The puncture and leak of tires are more prone to occur in the farmland cultivation.Once the puncture or leak of tire occurs,the device will sense the abnormality and send out an alarm signal in the first time.Thus the remedial measures can be carried out timely,avoiding delaying production and improving production efficiency.In this paper,the passive sensing device used in the automotive inspection,the application of piezoelectric power generation and the advantages of piezoelectric power generation were introduced,aiming at providing a theoretical basis for the intelligent control and utilization of piezoelectric vibrators.

Introduction of passive sensing device used in automotive inspection

Adirect tire pressure monitoring system (TPMS) powered by a microgeneration device was developed.Since the generating ability of the cantilevered piezoelectric vibrators is known higher than that of the simplysupported piezoelectric vibrators,the energy-converting devices were designed as the cantilever-type piezoelectric vibrators.The piezoelectric power generation is characterized by high voltage and low current.Moreover,the voltage is changed alternatively.So the power cannot be directly used for the load in most cases.If the piezoelectric power generation device is used for powering the alarm system,the power should be accumulated to some extent firstly and then can be used for powering the alarm system under the controlled circuit.

The power memories can be divided into 2 kinds:super capacitor and ordinary capacitor.These 2 capacitors all have their own advantages and disadvantages.The super capacitor is characterized by large capacity,long life and strong continuous-supply ability.However,the power leakage may occur.If the super capacitor is used in the piezoelectric power generation device,it must be fully charged before the use.This memory pattern can provide a continuous and stable power.However,it also has a series of deficients,such as self-discharge during the storage and long charging cycle.It cannot reach the working voltage in a short time.The ordinary capacitor has advantages of small capacity,long life and rapid charge and discharge.Therefore,we selected the ordinary capacitor as the energy memory for the alarm system.In the context of using the ordinary capacitor as the power memory,the control circuit was designed according to the working requirements by tire pressure alarm.The power produced by the excitation sensors in the piezoelectric power generation device can be accumulated effectively through the control circuit.When the accumulated power is enough to meet the demand of the tire pressure monitoring system (TPMS),the power will be discharged instantaneously,achieving the intelligent control and utilization of the piezoelectric power.

The main material of the mechanical energy/power conversion device of the piezoelectric power generation device is piezoelectric ceramic.When the external force is deformed,the electrode phenomenon will occur in the interior.At the same time,different polarization charges may be generated on certain surfaces.This electrode phenomenon within crystals caused by external forces or stimuli but without the assistance of external electric field is called as positive piezoelectric effect(referred to as piezoelectric effect).

The piezoelectric vibrator prepared with the piezoelectric material with piezoelectric effect is called as piezoelectric power harvester.Since the piezoelectric ceramic chips are hard and brittle and cannot be used as piezoelectric power harvesters directly,they are often alloyed with metal elastomers to produce the compound piezoelectric power generation devices.The piezoelectric vibrators can be made by two methods:(1)sticking the piezoelectric chips to the metal substrate with an adhesive; (2)sintering the piezoelectric material directly onto the substrate (the material of the substrate is silicon) to prepare compound film.

The excitation patterns of the piezoelectric vibrators include forced excitation and inertial excitation.The forced excitation refers to the external load or amplitude.Under the action of external load or amplitude,the piezoelectric vibrators are bent.Under this excitation pattern,the output voltage varies with the changes of excitation.The generating ability of piezoelectric vibrators is directly related to the strength of excitation.This excitation pattern is more suitable for the occasions that demand alternating excitation,especially for the long-term field or remote-area working conditions.The inertial excitation is also the free vibration of the piezoelectric vibrators when the free end of the spring-mass system composed of mass block and cantilevered piezoelectric vibrators is impacted or tapped.The generating ability of the piezoelectric vibrators is relatively weak under inertial vibration.However,the lasting time of the vibration is longer.This excitation pattern can absorb vibration energy in the environment and transform the energy without the participation of people,providing continuous power supply.

Currently,the ceramics used for producing generation-using piezoelectric vibrators are usually thin chips with thickness of 0.5-5.0 mm.The ceramic chips can be mass-produced by the piezoelectric ceramic chip cutter in industry.Since the ceramic chips are hard and brittle,a small thickness usually requires a small cutting area.However,the piezoelectric power is characterized by high voltage and low current.Under conditions of limited area of monomer piezoelectric ceramic chip,multiple chips or bimorphs are connected in series or in parallel to increase the generating ability of piezoelectric vibrators.

Based on the analysis on the tire structure,the piezoelectric vibrators have 2 possible installations in the tire.First,the piezoelectric vibrators can be attached to the surface of the rubber tire.When the tire contacts with the ground,the piezoelectric vibrators are deformed,generating power.Second,the piezoelectric vibrators can be mounted on the hub of the tire with rational mechanisms.Thus the vibration of the rolled tire can be used to generate power.

（2）在U型止水带上打孔，孔的大小和间距与止水槽内螺栓的尺寸及间距相符，止水槽找平后，在U型橡胶止水带下表面涂刷具有很好亲和性和变形协调性的环氧结构胶黏结材料，胶层厚不小于3mm，涂抹均匀完整，在环氧结构胶未凝固状态铺设止水带，逐段压实，直至止水带两侧有胶体溢出，使橡胶止水带与混凝土基面无缝对接，有效避免了止水带与混凝土基面的渗漏通道。

In the first installation,the piezoelectric vibrators will be deformed with the deformation of the tire.Their vibration is forced.Since the piezoelectric ceramic chips are hard and brittle,the piezoelectric ceramics are easy to fracture when the deformation of tire is too large.Even worse,this installation is not conducive to the exportation of electricity.Instead,all the problems above can be best solved if the piezoelectric vibrators are installed with the second installation.Under the second installation,the vibration of the tire(i.e.disturbance) will be transmitted to the piezoelectric vibrators by mechanical structure,ensuring the piezoelectric vibrators inertial vibration.Generally,the vibration frequency of tire ranges from 10 to 150 Hz,belonging to low frequency.Moreover,the vibration amplitude of the piezoelectric vibrators varies with the changes of the external conditions (road conditions,vehicle speed,etc.).Therefore,the selected piezoelectric vibrators must not only work under low-frequency conditions but also obtain a large deformation under different excitation pattern due to different supporting way.

For the piezoelectric vibrators,the excitation produced from the vibration of the hub is complicated during travelling.Since the excitation to the piezoelectric vibrators is continuous inertial force,it varies continuously with the change of vehicle speed and road conditions.So the designed piezoelectric power generation device should produce enough power for the TPMS under conditions of low speed and flat road.

The piezoelectric cantilever is the core component of the piezoelectric power generation device.A mass block will be attached to the free end of the cantilever to increase the mechanical energy input and improve the power output capacity of the piezoelectric cantilever.Meanwhile,the natural frequency of the mass block can also be adjusted by changing the mass of the block.In addition to the size,structure and excitation frequency of the piezoelectric cantilever,the end mass of the piezoelectric cantilever is also a key element affecting the output performance of the piezoelectric generator.

For the simplified models of the cantilevered piezoelectric generator and the metal-substrate and ceramiccantilever piezoelectric generator,the elastomer formed by the ceramic films is equivalent to spring.In addition,due to the presence of mechanical damping and material damping,the piezoelectric cantilever can be simplified as spring-mass system with viscous damping.Under conditions of ongoing external excitation,this system is a steady-state inertial vibration system.

The output power of the piezoelectric power generation device is limited,so it cannot be directly used for powering the TPMS.In order to solve the problem and improve the generating capacity of the piezoelectric power generation device under limited volume,the rectifier,memory and power supply control circuit must be installed at the output of the piezoelectric generator.Thus the electrical energy generated by the piezoelectric generator can be accumulated and the power output can be orderly controlled.

The piezoelectric power generation device is characterized by high voltage and low current.The voltage is changed alternatively.So the generated power cannot directly supply the load in many cases.In addition,the damping effect is existed in the energy output process of the piezoelectric power generation device.The accumulated energy will not only impede the further generation of charge but also hinder the further deformation of the piezoelectric vibrators.Therefore,the generated power should be accumulated first and then supply the TPMS under rational control circuit.The piezoelectric power generation in the tire is intermittent and discrete,and this requires that the storage device has a good repeated charge and discharge performance.The rechargeable battery is not suitable for collecting the energy generated by the piezoelectric power generation device.The super capacitor is characterized by large capacity(Farah),long life(repeated charge and discharge for hundreds of thousands of times)and continuous power supply (compared with ordinary capacitors).However,the leakage may occur in the super capacitor.The ordinary capacitor has small capacity,long life and fast charge and discharge.If the ordinary capacitors are used as memories,they are only suitable for the intermittentpower supply cases.

The receiving and displaying modules of the TPMS are installed in the cab.The CPU can calculate the temperature and pressure data inside the tire synchronously.When danger signs appear,the TPMS will alarm timely,ensuring the traffic safety.There are a total of 4 detecting and transmitting modules.They are installed on the hub for collecting,treating and sending pressure and temperature data inside the tire.

In order to improve the safety performance of the car,extend the life of tire and avoid the high temperature caused by friction between tire and inner tube,vacuum radial tire is generally used.The vacuum radial tire only has hub and tire but no inner tube.The rims are drop center rims.There are flanges on both sides of the rim,playing a role in fixing and sealing[1].The drop center will facilitate the assembly and disassembly of the tire.In the limited space,the piezoelectric vibrators are supported by cantilever and vertical to both the hub and the rolling direction of the wheel.This installing manner will increase the generating ability of the piezoelectric power generation device to the maximum extent.

Application of Piezoelectric Power

After decades of exploration on the generating characteristics of piezoelectric ceramics,the piezoelectric power has been successfully applied in different occasions.

Wang et al.have successfully transformed the mechanical energy into electrical energy in the nanoscale range.They have also researched and developed the most tiny nanoscale generator with vertical ZnO nanowires[2].

Priya developed a pocket-sized windmill which can supply energy for a wireless network.The windmill has an area of 8 cm2,and it is mounted on a rotatable cam[3].The rolled cam will make the attached piezoelectric crystals retract inward.In the squeezing or stretching processes,the piezoelectric material will produce electrical energy.A tiny wind speed of 32 km/h can produce a 15-milliwatts continuous power,which is much higher than the required power supply by the operation of an electronic sensor.The highest conversion efficiency of the windmill can reach 18%.However,the conversion efficiency of the same-size conventional generator is only 1%.

At abroad,the human generator accounts for the majority of the developed piezoelectric power generation devices.Among them,the piezoelectric power generating shoes are the most outstanding.These generating devices provide a promising development prospect for energy storage and piezoelectric power generating technology.Their generated powers are enough for the electronic devices used in the radio tracking and communication links.In the piezoelectric power generating shoes,the generating devices are installed on the soles,and the piezoelectric ceramics will be deformed by people’s weight in normal activities,therefore generating electrical energy.

In the early 2 000s,the road signs powered by the piezoelectric power generation device were developed in Japan.The plumes that are used for withstanding wind resistance are mounted on the surface of the signs.The weight-bearing balls,piezoelectric power converting device and several generating light sources are installed in the interior of the signs.The sub traffic signs can be placed in larger tunnels,and thus the wind energy can be used to roll the signs.When the weight-bearing balls hit the piezoelectric converting devices,electricity is generated.When the wind speed is higher than 3 m/s,the signs will shine once every 0.3 s with brightness of 4 000 mcd and each shining will last for about 3 ms.The tests and practical application all verify that the light can be seen within 200 m.

Kimura placed the emitters on the bodies of the birds.When the birds fly,the vibration of the wings can be used to drive the piezoelectric vibrators,generating piezoelectric signals.This patent can be used to determine the identification codes and the location information of the birds.

Advantages of Piezoelectric Power

In this paper,a new piezoelectric power generation device was developed based on the analysis on the output power and practical application of the generating devices in the TPMS.In addition,a new power supply management and control program was adopted.The circuit can be regulated automatically under a micro power.The interrupted working pattern of the piezoelectric power generation device can supply a relatively high current for the TPMS.

Compared to the current powering technologies for the TPMS,the piezoelectric power generation device is characterized by long-life battery,simplified installing and durability.Its capacity is affected slightly by temperature.The device has a high reliability.In addition,the life of battery is extended.

The piezoelectric energy recovery device was adopted.The mechanical energy and the electrical energy can be converted easily.The structure is simple and diverse.In addition,the running of the device is not affected by electromagnetic interference.The performance of the system is stable.The piezoelectric ceramics have a high energy density.Non pollution will be produced in the working process.The device also has a higher strength.However,the natural frequency is high,so the generating amount is not very high.The natural frequency of the generation device can be reduced by connecting multiple circular vibrators in series,aiming at improving the overall power output.The vibration-excited multiple vibrator-connected piezoelectric power generation device solves the problem of low-frequency vibration energy.The rotation-excited multiple vibrator-connected piezoelectric power generation devices solve the problem of passive sensing and monitoring of the rotating bodies.

The enhanced piezoelectric materials help to transform the mechanical energy of the rotating tires into electrical energy.In addition,the sensitivity of the TPMS to the tire pressure is also improved.Considering the energy storage,the ordinary capacitor is adopted to achieve the fast charge and discharge.This generation device is suitable for the interrupted-power supply occasions.It transforms the micro vibration into electrical energy,taking advantage of the usual tiny energy and turning waste into treasure.

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