MEASUREMENT METHOD AND DEVICE FOR VEHICLE DYNAMICS

Transcription

1 7h Inernaional DAAAM Balic Conference "INDUSTRIAL ENGINEERING" April 21, Tallinn, Esonia MEASUREMENT METHOD AND DEVICE FOR VEHICLE DYNAMICS Väljaos, E. & Sell, R. Absrac: This paper gives an overview of he iniial developmen of dynamic parameers measuring sysem and mehod for vehicles. Mobile roboic plaforms and vehicles driving abiliies in real environmen condiions are characerized and compared based on parameers ha are measured during real world condiion ess. The measuring resuls are used for comparison, developmen and improvemen of vehicle plaforms in heir design sage. Key words: Real-ime measuremen, mobile roboics, vehicle dynamics. 1. INTRODUCTION Differen vehicles driving performance can be compared beween each oher based on real condiion measuremens while recording heir posiion and acceleraion performance during ime es. Real-ime daa measured during driving reflecs he real world and are essenial o verify dynamic simulaions [ 1 ] or ess wih dynamomeers. Same daa can simulaneously be used for uning engine, ransmission and suspension parameers. If he vehicle is unmanned, he driving algorihms decision-making abiliies, flexibiliy and versailiy can be evaluaed. In opposie case, he driver skills can be improved and raed. The mos imporan measure of dynamical performance is driving acceleraion ha can be measured a minimum wih inerial navigaion sysem (INS) and speed or posiion can be calculaed. Usually addiional parameers like power, orque, driving loss esimaion, gear change and wheel slippage are needed for vehicle performance improvemen. These parameers are usually no direcly calculaed. The curren research inroduces he mehod and device which enables o measure he vehicle acceleraion and calculaes addiional parameers, based on he measured acceleraion in real-ime. There are some devices available in marke inended for simpler car performance esing, bu have usually specific onepurpose funcionaliy. Developed device [ 2 ] wih novel measuring mehod is aiming o cover wide range of dynamic parameer measuremens eiher an ordinary car or unmanned vehicle. 2. FRAMEWORK The research is a par of general mecharonic sysem design mehodology framework [ 3 ]. The framework is a new approach feaured by he model-based archiecure. This research provides he simulaion algorihms, which are developed and verified on he differen ypes of vehicles, saring from convenional cars o hybrid mobile robos. The measuremen mehod and resuls are unified o general mobile vehicle and will be used as a par of simulaion library of he design framework. The arge device of ongoing research is he mobile roboic plaform, bu he mehod and device can be fully used for any vehicle. The resul of his research plays imporan role of verifying he mobile robo simulaion algorihms and are used o develop auonomous navigaion scenarios [ 4 ] of roboic plaforms.

2 3. CALCULATION METHOD Usually he posiion in INS is calculaed using rigonomery and marices, bu his is complicaed o compue [ 5 ] and does no solve auomaic driving direcion deerminaion. The acceleraion of observed vehicles mus be measured for every direcion. The mos imporan is longiudinal driving acceleraion, which represens he maximum driving performance provided from engine or moor of a vehicle. The ransversal acceleraion is imporan for curved rajecory and verical for observing suspension characerisics. All hese acceleraion direcions assigned from vehicles body, mus be separaed and calculaed from hree-axis acceleromeer daa. As he measuring resuls are grealy affeced of sensor posiioning, daa has o be ransformed so, ha he posiion does no affec measuring resuls. To find he direcion of he sensor axes using graviy g, he mouning posiion deecing algorihm is implemened (Figure 1). If he device is fixed ino a vehicle firs he axis quiescen values a q( x) q( y) and a q( z) should be found wih averaging and daa recorded during es a (x) ( y) (z) is reduced using hem. Using only graviy, he plane T h can be found, where longiudinal and ransversal acceleraion vecors are locaed. Disinguishing hem is possible afer he driving es daa is recorded and maximum velociies v max(x), v max( y) and v max(z) on each axis are obained wih inegraing acceleraion daa. Therefore he coefficiens K v for each axis can be calculaed, which represens heir posiioning level in driving direcion: K v( x) vmax( x) = (1) v + v + v 2 max( x) 2 max( y) 2 max( z) As he axes of a sensor will form a sphere, he summarized acceleraion vecor for driving direcion can be calculaed for each ime samp: a = x K + y K + z K v( x) v( y) v( z) (2) Also he acceleraion daa obained from conroller analogous-digial converer (ADC) mus be ransformed ino real world unis. The sensor axes values corresponding o naural acceleraion a 1g ( x) 1g ( y) 1g ( z) can be measured by urning sensor 18 in each axis direcion and also calculaing zero acceleraion levels a ( x) ( y) ( z). T h a (x) a (z) Fig. 1. Driving direcion acceleraion a is calculaed from graviy and sensor axes measuremens. If only inerial measuring sysem is used, velociy v n and posiion s n daa for each ime samp n can be calculaed from acceleraion wih simple inegraion: n v n = a n i= 1 n s n = v n i= 1 (3) (4) As engine and suspension driving vibraion grealy affecs he measuring resuls, digial filering is needed. For dynamic daa, he Kalman filer is suiable. I can be much simplified for faser compuing wihou losing usabiliy and no o filer ou gear changes (Figure 2). During each ime bi, he daa can also be measured several imes and averaged before saving ino memory.. g a (y) a

3 7 5 Driving direcion acceleraion Π = P P (8) Acceleraion a, m/s Time, s Fig. 2. Example of filered acceleraion daa (car acceleraion wih one gear change). I is also necessary o record engine urning frequency ω. I can be measured wih imer from swiching frons of igniion coil or injecor or wih encoders in elecric moors. The power and orque for acceleraing vehicles body mass can be calculaed from acceleraion. As These are relaed o vehicles mass mcceleraion a and ime bi mean velociy v, he body mus be weighed. The power P a any given ime samp can be calculaed from equaion: P = m a v (5) I is possible o record vehicle deceleraion a afer aaining given speed and herefore esimae summary losses from air, rolling, ransmission ec. resisances. The resisive power P for vehicle acceleraion is: P ( a) v = m (6) As he resisive force F is growing wih velociy square and herefore he rendline for describing i can be calculaed wih roo mean squares mehod. If boh powers are recorded, he summary power available from engine oupu can be found: and summary loss is: P + = P P (7) If he engine urning frequency ω is also recordedcceleraing orque can be calculaed from power P: P T = (9) 2 π ω The resisive orque can similarly be found. One of he mos ineresing and novel issues accomplished by he developed measuring mehod, is a gear changing parameers calculaion. The gear change duraion is calculaed based on acceleraion daa for manual gearbox equipped vehicles and based on engine urning frequency for auomaic gearboxes. Anoher novely is o measure vehicles summary cluch and acceleraing wheels slippage. I is possible while comparing he acceleraions of a vehicle body and engine urning frequency and is imporan for racion or suspension and driver skills or driving uni maximum performance improvemen. Several anoher sensor daa can be fused ino measuremen process o find parameer correlaion facors and o improve hem from dynamic performance aspec. These are for example inner combusion engine parameers lambda, manifold pressure, inner emperaures, igniion and injecion parameers. 4. MEASURING ACCURACY INS is accepably precise for abou under 15 seconds measuremen ess, bu i can much be improved wih GPS correcion on longer ess. Inegraion from acceleraion measuremens for velociy and posiion acquiring is also consanly increasing heir error [ 6 ]. Wih only inerial measuring sysems i is also imporan no o encouner consan velociy.

4 Anoher aspec is vehicle body deviaion compared o wheels, while saring driving. Alhough inner combusion engine adds more noise and vibraion ino measuremens (igniion wires, generaor), elecric moor have also negaive elecromagneic effecs. Oher sources of unavoidable errors have effec on es repeaabiliy, bu no for calibraion procedure as hey have equal impac on ealon device. Unknown error is added from driver or driving sysem behaviour, which yields o differen resuls on same esing rack. Engine emperaures are also varying while driving and herefore oupu power. Oher errors are from real world couneracions, like variable windir emperaures and rack properies. These effecs can only be minimized if ess are carried ou quickly or condiions measured. All measuremens ha are calculaed based on acceleraion daare dependen from consan parameers for given measuremen naural acceleraion g, quiescen acceleraion a q, zero-acceleraion level a and he measure on naural acceleraion a 1g for each sensor axis. The errors of hese consans can be minimized wih careful sensor calibraion procedures. The oher variables are measuremen ime ll acceleraions up o given ime a and engine urning frequency ω. The power P and orque T is affeced from mos variables involved in measuring sysem: P = f, g, a, ) (1) ( a lg 1g ω Calibraion mehod is based on measuring he same objec wih ealon device [ 7 ] (Figure 3). The ealon device can be infrared laser based iming sysem insalled ino suiable lengh road rack. The iming sysem is more accurae when measuring elapsed imes wih vehicle wheels inerruping infrared beams. However he errors are here uncerainy of rack lengh, sensor posiions and saring poin as i can vary o lengh of wheel diameer. Ealon (iming sysem) x e x m Objec (road rack) x m Fig. 3. Device calibraion model. Measuring device x y =x e x 5. MEASURING EQUIPMENT DEVELOPMENT For esing and improving measuring mehod, he pracical elecronic device was consruced for carrying on ess in real world condiions on differen vehicles. As he microelecronics is consanly evolving, he grea measuring, recording and compuing capaciy can be packed ino very small mobile phone like device (Figure 4). Volage converer RTC + Li-baery 3-axis acceleraion sensor Opocoupler Flash-memory Microconroller 8-bi Swich Swich Swich Swich Fig. 4. Tesing device block-diagram. LCD USBdriver The iniial version of a esing device is based on AVR 8-bi microconroller working on MHz frequency, ± 19.6/58.9 m/s 2 MEMS acceleraion sensor wih 12/16-bi ADC, backlighed LCD and an opocoupler. The daa is recorded on 2 Hz frequency o 1 MB flash memory. For giving ime samp o each measuremen, he real-ime clock (RTC) uni wih rechargeable Li-baery is used. Opocoupler is used for measuring engine revoluions, which enables o calculae he orque of driving wheels. The recorded daa can be ransmied o PC via USB.

5 The whole device (Figure 5) was made very ligh and small and is herefore mounable o any vehicle saring from moorcycles or small roboic plaforms. Speed v, km/h Driving direcion speed Time, s Fig. 6. Calculaed car speed wih gear changes (Audi S2 94). 5 Driving direcion disance Fig. 5. Tesing device finished. 6. EXPERIMENTAL RESULTS Disance s, m Pracical examples wih he developed device for esing measuring mehod were carried ou wih regular cars. The esing ensured ha he developed posiion correcion worked wih good resuls. Table 1 shows, ha even mouning he device a differen posiions only small deviaion arise. X / % Y / % Z / % v calc / km/h,8 99,2 61 3,1 96, , 55, 62-28,8 71,8 62-9,5-13,3 77, ,5 57,5 61,9 36,2 62,9 62 Table 1. Calculaed speeds from acceleraion wih differen device posiions. For aaining differen speeds and measuring rack lengh elapsing imes, he device showed good repeaabiliy 1 2 % depending on driver s success. The resuls were comparable wih laser iming sysem resuls being differen under 2 %. Experimenal resuls of calculaed parameers are shown on he Figures Time, s Fig. 7. Calculaed car covered disance. Frequency ω, r/min Engine urning frequency Time, s Fig. 8. Recorded engine urning frequency. Power P, kw Acceleraing power Turning frequency ω, r/min Fig. 9. Calculaed acceleraing power depending from engine urning frequency.

6 7. FUTURE DEVELOPMENT The research has so far had a pracical oupu for finishing firs esing device and having also good opporuniy o become commercial produc. For esing equipmen developmen, he GPS module will be involved for posiion correcion. The daa of he sensors will be fused ogeher for improved acknowledgemen of vehicles dynamics simulaneously involving oher sensors daa (emperaures, pressures, volages). For vehicles where enormous noise and harness is usual, he CAN inerface for sensor nework is suiable for measuremen accuracy improvemen. If i is also needed, even greaer compuing and recording capaciy can be implemened using 32-bi microconroller and Secure Digial (SD) flash memory cards. According o he resul of using he mehod and device wih convenional cars he soluion will be adaped o he unmanned roboic plaforms. The measuremen mehod will be furher developed o implemen i for vehicles wih differen moving mehods, enabling o acquire real daa of he specific robo plaform and compare i wih resuls of simulaions. This enables o improve he simulaion algorihm in library and prove is compaibiliy wih real siuaion. 8. CONCLUSION As a conclusion, he suiable measuremen mehod basis for boh manned and unmanned vehicle dynamics was developed and successfully esed. The mehod accomplished auomaic posiion correcion and driving direcion sensing algorihms, which are essenial for reliable measuremen. The mehod enables o acquire many differen characerisics for comparing vehicles or uning heir driving abiliies. The developmen succeeded o pracical esing device ha is capable for accomplishing given asks wih good resuls. 9. ACKNOWLEDGEMENT This research was suppored by he Esonian Scienific Foundaion gran ETF7475 and Esonian Minisry of Educaion and Research Projec SF14113Bs8. 1. REFERENCES 1. Shor, M. Pon, M.J. Huang, Q. Simulaion of Vehicle Longiudinal Dynamics. Embedded Sysems Laboraory, Leiceser, E. Väljaos, Device for measuring vehicle dynamics. M.Sc. hesis, Tallinn Universiy of Technology, Tallinn, Chrisophe, F., Sell, R., Coaanéa, E. Concepual design framework suppored by dimensional analysis and Sysem Modelling Language. Esonian Journal of Engineering, Tallinn, Sell, R., Leomar, P. Universal Navigaion Algorihm Planning Plaform for Unmanned Sysems. In: Proc. of Inernaional Conference Mecharonic Sysems and Maerials, Vilnius, Woodman, O.J. An Inroducion o inerial navigaion. UCAM-CL-TR- 696, Universiy of Cambridge, Cambridge, Grewal, M.S. Weill, L.R. Andrews, A.P. Global posiioning sysems, inerial navigaion and heir inegraion. A John Wiley & Sons Inc, Hoboken, Laaneos, R. Mahiesen, O. Mõõmise alused. TTÜ Kirjasus, Tallinn, CORRESPONDING ADDRESS Eero Väljaos. Deparmen of Mecharonics, Tallinn Universiy of Technology. Address: Ehiajae ee 5, 1986 Tallinn, Esonia. Phone: eero.valjaos@englo.ee