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Piezo electric power generating shock absorber


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Piezo electric power generating shock absorber

  1. 1. PIEZO ELECTRIC POWER GENERATING SCHOCK ABSORBER ABSTRACT: When used in a vehicle or hybrid electric vehicle the electricity generated by the shock absorber can be stored in the battery to be used later. In non-electric vehicles the electricity can be used to power accessories such as air conditioner. The two designs that we had considered for conserving energy from shock absorber are: 1) Electromagnetic 2) Hydraulic 3.1 ELECTROMAGNETIC The design consists of two tube-like components - a hollow copper coil assembly and a magnet that uses vibration of the vehicle’s suspension to move up and down inside it. When the vehicle is in motion, the vibration in the suspension causes the coil to move relative to the magnet. As the copper coil moves inside this magnetic field, a voltage is generated. But this design is not much efficient due to the losses. The power is lost in the form of eddy current loss and hysteresis loss. Also the system tends to be bulky and cannot be successfully implemented in smaller shock absorbers of two wheelers. ECWAY TECHNOLOGIES IEEE PROJECTS & SOFTWARE DEVELOPMENTS OUR OFFICES @ CHENNAI / TRICHY / KARUR / ERODE / MADURAI / SALEM / COIMBATORE BANGALORE / HYDRABAD CELL: 9894917187 | 875487 1111/2222/3333 | 8754872111 / 3111 / 4111 / 5111 / 6111 Visit: Mail to:
  2. 2. 3.2 HYDRAULIC This design consists of a hydraulic system that forces fluid through a tiny turbine attached to a dynamo. Each time the shock absorber compresses, the fluid is forced through the turbine causing it to rotate. Thus energy is generated in the coupled dynamo. The main disadvantage of this method is that it can be used only in heavy vehicles. 3.3 OUR CONCEPT In our design, the energy is regenerated using a piezoelectric crystal. A piezoelectric crystal is installed within the shock absorber. When the shock absorber is compressed, force is transmitted to the piezoelectric crystal. Thus electric energy is obtained from the shock absorber. The force transmitted to the piezoelectric crystal is limited to the safe range of the material by using suitable damping mechanism. The design considerations of the piezoelectric shock absorber are explained in the next chapter. The piezoelectric regenerative shock absorber can be used in any vehicle, irrespective of size ranging from two wheelers to trucks. Piezoelectric crystal of appropriate size is fixed on the shock absorber. By recovering the vehicle’s energy lost in vibration, the piezoelectric regenerative system will be able to increase fuel efficiency in a hybrid or electric powered vehicles. In other vehicles the pulsating voltage obtained from the shock absorber can be rectified by using a rectifying circuit and can be used to charge the battery. This can be used to power other accessories in the vehicle.
  3. 3. CHAPTER-4 DESIGN AND ANALYSIS 4.1 DESIGN A cylindrical shaped piezoelectric material (PZC), made of Lead Zirconate Titanate Ceramic, commercially known as DCPL-5 is fixed within the shock absorber, with suitable damping so that only a part of the total force generated while shock absorber compression is transmitted to the PZC, sufficient enough to generate the optimum voltage, with a constraint on the maximum endurance strength of the material. Ceramic PZCs usually have high compressive yield stress. The rough arrangement of components will be as shown- Fig 4.1. Proposed design of the shock absorber (The outer spring is omitted in the diagram to show the inner components) PZC Bush Spring
  4. 4. 4.1.1 DCPL-5 It is a modified Lead Zirconate Titanate Ceramic, providing transducer elements with high electro mechanical coupling coefficient and high charge sensitivity and curie temp of 350 º C, used for sensing applications like ultrasonic flaw detection, under water echo sounding, pressure gauges, strain gauges, accelerometers, medical Instruments, flow meters, NDT systems, Level gauges and many other devices. Our model was developed using this crystal, which was sent to us by Mr. Sunil Kapoor, Doon Ceratronics Pvt. Ltd, Dehradun, on request. The properties of the PZC is tabulated as- Properties Symbol DCPL-5 Piezoelectric Coupling Coefficients Kp .60 K33 .70 K31 .32 Piezoelectric Charge Coefficients(x 10-12 C/N) d33 425 d31 -170 Piezoelectric Voltage Constants (x 10-3 Vm/N) g33 25 g31 -11 Dielectric Constant at 1Khz KT33 1750 Dissipation Factor .02 Mechanical Quality Factor Qm 75 Density (Kg/m3 ) 7650 Curie Temperature (Tc) °C 350 Frequency Constants(Hz-M) Np 1950
  5. 5. Important factors governing performance are the shape of the PZC transducer, the manner in which the transducer is mounted and, of course, the nature of the electrical load. A PZC disk for example, compressed between two metal surfaces will never be able to expand in the radial direction as readily as would a long, thin cylinder, which is only constrained at its ends and assumes a barrel shape on radial expansion. So the way in which the material is mounted will directly affect the energy conversion per unit volume. The general rule therefore is to allow the PZC body some freedom to expand radially since charge generation is directly coupled to deformation. 4.2 ANALYSIS Assuming the force on the PZC to be static, the following analysis is carried out Consider a PZC cylinder of height h, polarized in the axial direction and with electrodes on its end faces. If an axial stress T3 is applied, it will deform and hence charge will displace toward the electrodes. Under open circuit conditions (D = 0) the voltage U3 is given by: U 3 = - g33hT3 -- (1) A compressive stress (negative sign) will therefore generate a positive voltage across the transducer. To get an idea of the order of magnitude of the voltage to be expected, a 10 mm Lead zirconatetitanate cube (g33 = 22 x 10-3 Vm/N) subjected to a force of 5kN will generate a voltage about 11 kV. The total energy WD fed into a PZC element by a mechanical source can be split up as follows: (no losses, open circuit) W D = Wm + We -- (2) Where: Wm = mechanical deformation energy.
  6. 6. We = energy stored in the electrical field in the ceramic. The latter may be withdrawn from the element as electrical energy. The energy WD can be simply expressed in terms of compliance SD and the mechanical stress T by: In which V is the volume of the PZC element. We and Wm are given in terms of the coupling coefficient k33 by: These equations show that for given material properties only V and T govern the energy conversion. If, therefore, in a particular application the force that can be applied is limited, the electrical energy generated can be increased by choosing a smaller surface area (equal volume). For example one can use a long thin cylinder instead of a short thick one. PZC-elements under compressive stress in open circuit conditions do not suffer from depolarization. The induced field has the same direction as the poling field during polarization and the voltage increases almost linearly with the stress even up to very high load levels. = = =
  7. 7. Fig 4.2. Charge density on PZT5A discs as a function of compressive load. The discs (h = 5 to 16 mm) were clamped between two steel plates. The PZC, springs and bushes are fixed on the shock absorber in such a way that the total stiffness and hence the performance of the shock absorber as a whole is not affected. A typical shock absorber can be shown by the following line diagram:- Fig 4.3. Line diagram of the system
  8. 8. Where K is the stiffness of the outer spring and c is the damping coefficient of the dashpot (air chamber). Suppose we have an impressed oscillating force F=F0sinωt, causing a displacement x1 which is a function of time, t. Inertia force = mẍ Damping force = cẋ Spring force = kx Thus equation of motion will be- mẍ + cẋ + kx - F0sinωt = 0 Or mẍ + cẋ + kx = F0sinωt The complete solution of the equation consists of two parts, the complementary function (CF) and the particular integral (PI). CF = Xe-ξωnt sin (ωdt+Φ1) Where, X and Φ1 are determined from the initial conditions, ξ is the damping factor, ωn is the natural frequency of the system, ωd is the damping frequency which is related to ωn as :- ωd = 𝜔 𝑛√1 − 𝜉2
  9. 9. To obtain the PI, let c/m=a, k/m=b and F0/m =d Then using the operator D, the equation becomes, (D2 +aD+b)x =d sinωt PI = 𝑑 𝑠𝑖𝑛𝜔𝑡 𝐷2+𝑎𝐷+𝑏 PI = 𝑑 𝑠𝑖𝑛𝜔𝑡 −𝜔2+𝑎𝐷+𝑏 = 1 (𝑏−𝜔2)+𝑎𝐷 × (𝑏−𝜔2)−𝑎𝐷 (𝑏−𝜔2)−𝑎𝐷 𝑑𝑠𝑖𝑛𝜔𝑡 = 𝑑 [ 𝑠𝑖𝑛𝜔𝑡(𝑏−𝜔2)−𝑎𝐷𝑠𝑖𝑛𝜔𝑡 (𝑏−𝜔2)2+ (𝑎𝜔)2 ] Taking ( 𝑏 − 𝜔2)=RcosΦ and aω =RsinΦ, on further simplification yields :- PI = 𝐹0 √(𝑘−𝑚𝜔)2+(𝑐𝜔)2 sin(𝜔𝑡 − 𝛷) x = CF + PI x = Xe-ξω n t sin(ωdt+Φ1) + 𝐹0 √(𝑘−𝑚𝜔)2+(𝑐𝜔)2 sin(𝜔𝑡 − 𝛷) -- (1)
  10. 10. This is the equation of displacement of an unmodified shock absorber. Now we introduce the new components within the shock absorber to incorporate the PZC. Let the collective stiffness of the PZC, the two bushes and the two springs be Ke 1 𝐾 𝑒 = 1 𝐾 𝑝 + 2 𝐾 𝑏 + 2 𝐾𝑠 where, Kp is the stiffness of the PZC Kb is the stiffness of the bushes Ks is the stiffness of the spring. The modified line diagram will be as :- Fig 4.4. Line diagram of the modified system K 1 Ke
  11. 11. Suppose we have the same impressed oscillating force F = F0sinωt, causing a displacement x1 which is a function of time, t. Inertia force = mẍ1 Damping force = cẋ1 Spring force = K1x1 Force due to the new system = Kex1 Thus equation of motion will be- mẍ1 + cẋ1 + (K1+Ke)x1 - F0sinωt = 0 or mẍ1 + cẋ1 + (K1+Ke)x1 = F0sinωt The complete solution of the equation consists of two parts, The complementary function (CF) and the particular integral (PI). CF = X1e -ξ1ω n1 t sin(ωd1t+Φ1) Where, X1 and Φ1 are determined from the initial conditions, ξ1 is the damping factor, ωn1is the natural frequency of the system, and ωd1 is the damping frequency which is related to ωn as :- ωd1 = 𝜔 𝑛√1 − 𝜉1 2 To obtain the PI, let c/m=a, k/m=b and F0/m =d
  12. 12. Then using the operator D, the equation becomes, (D2 +aD+b)x = d sinωt PI = 𝑑 𝑠𝑖𝑛𝜔𝑡 𝐷2+𝑎𝐷+𝑏 PI = 𝑑 𝑠𝑖𝑛𝜔𝑡 −𝜔2+𝑎𝐷+𝑏 = 1 (𝑏−𝜔2)+𝑎𝐷 × (𝑏−𝜔2)−𝑎𝐷 (𝑏−𝜔2)−𝑎𝐷 𝑑𝑠𝑖𝑛𝜔𝑡 = 𝑑 [ 𝑠𝑖𝑛𝜔𝑡(𝑏−𝜔2)−𝑎𝐷𝑠𝑖𝑛𝜔𝑡 (𝑏−𝜔2)2+ (𝑎𝜔)2 ] Taking ( 𝑏 − 𝜔2)=RcosΦ and aω =RsinΦ, on further simplification yields :- PI = 𝐹0 √((K1+Ke)−𝑚𝜔)2+(𝑐𝜔)2 sin(𝜔𝑡 − 𝛷) x1 = CF + PI x1 = Xe-ξ1ω n1 t sin(ωd1t+Φ1) + 𝐹0 √((K1+Ke)−𝑚𝜔)2+(𝑐𝜔)2 sin(𝜔𝑡 − 𝛷) --- (2) The spring displacements in the two cases should be the same. Hence (1) = (2), which implies,
  13. 13. K = K1 + Ke K1 = K - Ke By measured data we have, Stiffness of Original the outer spring, K = 12.80 N/mm Combined stiffness of the inner springs, bushes plates and PZC, Ke = 2.25N/mm We design a new outer spring of stiffness K1 = K – Ke. The length and diameter of the spring remains unchanged. Number of turns of the original spring = 17 Number of turns n = 𝐺×𝑑4 8𝐷3 𝐾1 G = 8 × 104 N/𝑚𝑚2 d = 7mm D= 28mm K1 = 12.8 – 2.25 = 10.55N/mm On solving we get, n =18.197 n’ = n+2 = 21 turns (for squared and ground ends) Thus the outer spring, currently in use is replaced by another spring of the same material and dimensions with a slight change in the number of turns.
  14. 14. 4.3 RESULT The present model was tested with a CRO to find out the output. Screenshots of the CRO are as- Fig 4.5. Screenshots from the CRO The X- axis shows time in milliseconds and Y- axis shows voltage in volts. The energy generation is limited to a few fraction of a second, when the impact loading takes place. The graphs show a peak generated voltage of up to 25 V, when subjected to shock manually. The voltage generated depends on the force applied.
  15. 15. CHAPTER 5 CONCLUSION The use of piezoelectric crystal in the shock absorber is a new method for power generation. By using PZCs, power could be generated more effectively than that compared to electromagnetic and hydraulic type generation. The piezoelectric regenerative shock absorber can be commercialized for the use in vehicles. Also the cost involved is very low which makes it economically efficient. This technology can be efficiently implemented in conventional vehicles as well as electric and hybrid vehicles, which will be the future of automobile industry. The energy regenerated by the shock absorber by this method can be found out by calculating the current being produced. In order to calculate current, the Voltage vs. Time curve needs to be a continuous curve, for which a continuous load has to be applied without damaging any of the components designed in the shock absorber, especially the piezoelectric material. A special mechanism will have to be designed for applying this load which is well beyond the scope of mini project. The damping system can also be further improved by providing the optimum stress for maximum energy generation within the safe range of the ultimate stress of piezoelectric crystal. There is still room for a lot of improvement with this concept. It can be used in all vehicles to conserve the energy that goes waste, which though small, will be precious in the years to come, thus turning potholes into energy advantage.
  16. 16. ANNEXURE - I We have used bulk ceramic (commercially known as DCPL- 5) for our model. This is cheap and has high compressive strength. But the output is not very high. Fig AI.1 DCPL-5 bulk ceramic AI.1 MULTILAYER GENERATORS The technique developed to make multilayer capacitors can also be used for piezoelectric ceramics. Thin layers of so called green ceramic are interleaved with silver-palladium electrodes, compacted, cut to size and then sintered. With these devices, the large total surface area per unit volume means that the generated charge is high whereas the voltage is rather low. These types of generator are ideal for use as a solid state battery for modern electronic circuits.
  17. 17. Fig AI.2. Multilayer piezoelectric material Fig AI.3. Output voltage as a function of compressive load These multilayer piezoelectric crystals can be used in place of bulk ceramic for higher energy generation.
  18. 18. ANNEXURE II COMPARISON OF SHOCKS These notes identify the high force that can result from and impact and the show the reduction in force by use of a spring and a compensating hydraulic shock absorber. The example is provides as a general illustration and is very much simplified. Force resulting from impact with no shock absorber included Considering a very simple duty of dropping a 1 kg load through 1m onto a machine element represented by a short steel column 0.1m dia by 0.2m long made form steel. Fig AII.1.
  19. 19. The stiffness of the column k = AE / l. A = 0.00784m2 E = 21x1010 Pa (N/m2) l = 0.2m The stiffness of the column k is the Load /unit deflection is calculated as:- k = 0.0784 × 21 × 1010 /0.2 = 8.25 × 1010 N/m To calculate the maximum force resulting from the dropped load assuming conservation of energy. The strain energy absorbed by the column = the Potential energy absorbed from the dropped load. The potential energy of the load = E 1 E 1=Mgh = 4.905 Nm. This equals the strain energy absorbed by the load at impact The strain energy absorbed = Pmaxδmax /2 = Pmax 2 / 2 k Therefore to calculate the maximum force developed Pmax Pmax = Sqrt (2.E1.k) = Sqrt (4.905×8.25×1010 ) = 899kN Maximum force Resulting From Use of Spring If a spring with a stroke of 0.1m is located on the top surface as shown below
  20. 20. Fig AII.2 The resulting maximum force is determined as follows. Energy to be absorbed = E1 = Mgh. = 4.905 Nm Strain energy of spring = Fδspring /2 Therefore Maximum force = 2Mgh/δspring = 98.1N Use of the spring has reduced the maximum force by a factor of 10. However the spring is now exerting an upwrd force which will cause the load to rebound upwards. Detailed analysis of the system response is required to arrive at the total motion history of this event Maximum force resulting from the use of a compensating Hydraulic Shock absorber If a Shock absorber with a stroke of 0.1m is located on the top surface as shown below -
  21. 21. Fig AII.3 It is assumed that the shock absorber is designed to provide a constant deceleration force throughout its stroke.. The resulting maximum force is determined as follows. Energy to be absorbed = E1 = Mgh. = 4.905 Nm Energy to be dissipated in the shock absorber = Fδsh_ab Therefore Maximum force = Mgh/δsh_ab = 49.05 N The energy has been dissipated in heating up the hydraulic fluid in the shock absorber. When the load has come to rest the system is in a stable state. The maximum force transmitted to the column during impact is 1/20 that experienced by without the shock absorber.
  22. 22. REFERENCES 1. 2. 3. 4. 5. Theory of machines – S.S Rattan 6. Machine Design – S. Md. Jalaludeen 7. Design data book of engineers – PSG College of technology, Coimbatore