Raksit THITIPATANAPONG Embedded System Tech. Res. Lab., National Electronic & Computer Technology Center, Thailand

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1 A 150-kW Low Cost Engine Hydrostatic Dynamometer: Design and Feasibility Study Raksit THITIPATANAPONG Embedded System Tech. Res. Lab., National Electronic & Computer Technology Center, Thailand Montien KAENSON and Sataporn KLYLUNG Automotive Engineering Department, Faculty of Engineering, Sripathum University, Thailand ABSTRACT In Thailand, dynamometer needs to be imported, and it is a specific equipments which not commercially sale. In addition, the cost of dynamometer is relatively expensive which general mechanics cannot afford it. In this paper, the hydrostatic dynamometer was proposed as low-cost dynamometer for Thailand. This type of dynamometer equipped with commercial hydraulic part that widely used in industrial process. A 150-kW of dynamometer that equipped with hydrostatic devices were introduced and designed. Moreover, It could absorb torque more than 400 N.m. The hydraulically axial piston pump, sized 68 cc/rev, was applied in collaborate with electronically control pressure relief valve for the load controlling. It cost approximately Bth362,000 which 8 times cheaper than the import equipments. INTRODUCTION Dynamometer is a mechanical power measurement device that plays an important role in research and development especially internal combustion engine. The engine modification for alternative fuel needs dynamometer to simulate engine's load during tune-up. In general, dynamometer works with energy absorption from engine, simultaneously, it is capable to measure both torque and rotational speed. Moreover, dynamometer can be classified by methods of energy absorption which are hydro-kinematics, hydrostatic, and electrical. Each system has different characteristics that shown in table 1. Each type of dynamometer has advantages and disadvantage that needs to match in each application. [1] Hydro-kinematics or Hydraulic dynamometer uses the fluid viscosity as energy absorption media. This type of dynamometer operates with 2 main component, stator and rotor that submerge under water. The rotor drives the fluid and setup the centrifugal force. The effect is to transfer the momentum from the rotor to the stator and develop reaction torque to rotating shaft. The turbulent shear force from the fluids (water) dissipates the power in form of heat in fluids. This type of dynamometer has limited torque absorption at low rotating speed and nonlinear control but it can withstand excessive rotating speed. While the cost is comparatively low to others type of dynamometer Another fluid working dynamometer is hydrostatic system that apply resistance torque form positive displacement pump which drive torque directly relate to hydrostatic pressure of fluid output from pump. This system has advantages that absorb torque at low speed to stagnation and low inertia. Also, it can drive the tested engine. However, hydrostatic dynamometer is not widely use because operating and maintenance cost is higher than other systems For electrical system, the dynamometer can classify in 3 main types which are D.C. motor, A.C. Motor and eddy current brake. Firstly, Direct Current dynamometer is equipped with direct current motor and power rectifier which is an advantages on low speed torque but it is not recommend on operating at high speed due to contacted bush at rotor. Secondly, the A.C. system equipped with A.C. motor and inverter which characteristics like D.C. System but it can operate at high speed because there is bush less. Both types of motor dynamometer share advantages are easy to operate automatically, capable to drive tested engine and electrical energy generation from absorb energy. However, the electrical power control equipments are relatively large and expensive. Thirdly, the most widely used, eddy current brake system operates on magnetic induction to create resistance torque and dissipate energy into heat. This system has advantages on low power consumption and automatically control but it cannot drive tested engine. 1

2 Table 1 main characteristic of dynamometers Character/Type Eddy Current Electric Hydro-kinematics Hydrostatic Speed limit High DC: Medium AC: High None High depended on pump Applicable Torque Range (Speed) Low - High DC: Low Medium AC: Low - High Medium - High Very Low - Medium Polar Inertia Moderate High Low Very Low Size (at same capacity) Moderate Large Moderate Small Transfer Function Linear Linear Non-linear Linear Control Electrical Current Electrical Frequency/Current Mechanical/ Electrical Mechanical/ Electrical Regenerative No Yes No No (option) Drive No Yes No Yes (option) Maintenance Low Low Moderate High In Thailand, dynamometer is not general equipments that widely use by mechanic. It only limit to university or research institute. Moreover, all of them has to be imported from abroad and faces the maintenance and after-sale services problems due to lack of authorized dealer. In case of hydrostatic dynamometer which mention in this paper, although dynamometer package is not available, hydrostatic pump and hydraulically controlled valve that equipped in system are available because they are main component in machinery in industrial process that has many dealer and distributor including service and maintenance capability. There is a possible for this system to be a low-cost dynamometer for Thailand. In this paper, 150-kW engine dynamometer with hydrostatic system is designed including the feasibility study for internal combustion development. HYDROSTATIC DYNAMOMETER Lanti and Moskwa [2] introduced the hydrostatic dynamometer that applied hydraulic pump couple with single cylinder engine because, for low speed testing, the conventional eddy current dynamometer cannot test due to high polar moment of inertia. Another cause is that inconsistence power output of single cylinder engine at low speed which normally solved by applied flywheel but cause more problem in transient test. The positive displacement pump has been proposed to work as dynamometer on single cylinder engine test that capable to generate torque resistance at low speed with low polar moment of inertia. To simulate the real multi-cylinder combustion process, the hydrostatic controlled hardware and software have been developed on this single cylinder test engine with HIL (Hardware In the Loop) technique. [3,4,5] In earlier study [6], the 18-kW hydrostatic dynamometer has been compare the cost to hydraulic dynamometer and eddy current brake which has found that domestically fabricated hydrostatic system was 2 to 10 times lower cost than conventional imported dynamometer. Furthermore, the simulation study on hydrostatic system using commercial hydraulic software was done on both type of dynamometer operation strategies that were constant speed control with flow regulator valve and constant torque control with pressure relief valve. The simulation result showed that, the system pressure was directly related to torque resistance at engine but it was vary on the shaft rotational speed. In addition, the response time of hydrostatic system was very satisfied. In the experimental study, the results showed the limited on flow regulator controlled strategy in hydrostatic dynamometer control. On the other hand, the pressure relief valve strategy showed an excellent load control with adequate dynamic respond. However, the most disadvantage was torque measurement that needs expensive sensor but its still less cost than imported dynamometer. 2

3 HYDROSTATIC SYSTEM DESIGN DESIGN CONSIDERATION The design specification of this dynamometer is for R&D small truck engine which shown in table 2, so, the dynamometer system should absorb torque not less than 350 N.m and working speed not less than 3,500 rpm. Table 2 Taget Engine Specifications Engine Type Toyota 1KD-FTV, 3.0 L Diesel Engine Max. Torque Max. Power 343 N.m@1,400-3,200 rpm 120 kw@3,400 rpm HYDRAULIC PUMP SIZING The heart of hydrostatic dynamometer is the positive displacement pump. The special characteristic of positive displacement pump that apply in high pressure hydraulic system, the flow rate of hydraulic fluid does not depend on the pressure difference across pump inlet and outlet, the load can be easily predicted than other type of pump. [7] Theoretically, torque (T th, N.m) at pump's shaft is directly related to pressure across pump (P, Pa) as shown in equation 1 V P T = D th (1) 2π where V D is pump displacement (or positive displacement pump's size) in cc/rev which the power of pump can be estimated from equation 2 VD P N Power = (2) 60 where N is rotational speed in round per minute (RPM). Moreover, the flow rate across pump is directly related to rotational pump shaft speed as shown in equation 3 = V π (3) 2 N D 60 In practical, the pump may has some loss such as leakage of the hydraulic fluid, friction of bearing and fluid head loss. From the design consideration in table 2, the estimate pump size from eq. 1, at 350 bar operating pressure, is not less than 63 cc/rev HYDROSTATIC DYNAMOMETER DESIGN In general, engine dynamometer that operate in R&D facilities need to be controlled in 2 main strategies which are constant load control and constant speed control. From earlier studies [6], the pressure relief valve was recommended to control amount of load. Consequently, the hydrostatic controlled valve, the pressure relief valve with electro-mechanical drive is selected as main actuator. The computer data acquisition (DAQ) is apply for feed back control in both strategies from rotational speed sensor and torque sensor. The hydraulic components configuration as shown in figure 1 are air cool heat exchanger, oil filter, reservoir tank, and check valve. As sizing are recommend in table 3 from [8] Table 3 auxiliary equipment requirements Item Requirements Reservoir Tank 250 L Heat Exchanger More than 75 kw Pressure Relief Valve More than 300 liter Briefly estimation, this hydrostatic dynamometer system could capability to handle the 150 kw engine. EQUIPMENTS AND COST ESTIMATION In this study, the acquisition of equipments and components from local distributor and dealer are main interested, as they are expertise in services and maintenances the hydraulic system. The components can be deviled into 2 parts which are (1) hydrostatic equipments and (2) measurement and control equipments. The graphical model is illustrated in figure 2 HYDROSTATIC EQUIPMENTS The main equipments are listed in table 4. the tandem axial piston pump, size 2 34cc/rev, with electro-hydraulically control pressure relief valve are employed which cost Bth262,000. MEASUREMENT AND CONTROL For the measurement as lists in table 5, the dynamometer needs to sense torque and rotational speed. The mechanical differential gear is designed to measure rotating torque via load cell while the rotational speed is sensed by proximity sensor. Furthermore, the standard calibrating equipment also provide that is torque transducer, KISLTER 4502A500RA, as a reference in both torque and speed. 3

4 Figure 1 schamatic diagrame of hydraulic system control for hydrostation dynamometer Figure 2 graphical model of the system 4

5 Then, all measurement signal are logged to computer data acquisition system (DAQ) via LabView Signal Express. Hence, processed signals are used for automatically controlled dynamometer to electro-hydraulically pressure relief valve in both constant load and constant speed control. COST From table 4 and 5, it can be seen that workable dynamometer cost just Bth362,000 while calibration torque transducer cost Bth224,000 or 35% of total project cost as shown in figure 3. The large number of built can share cost of calibrating devices. Table 4 Hydrostatic Equipments equipments model specifications Cost (Bth) pump BONDIOLI&PAVASI M4PV cc/rev 350 bar (operate pressure) Max Speed 3,800 RPM 272,000 Controlled valve DUPLOMATIC RQM5-P bar 400 L/min Electrically Control Table 5 Measurement and Control Components Components model specifications Cost (Bth) Torque Transducer KISTLER 4502A500RA N.m Accuracy 0.2% Rotational Angle 224,000 Computer+DAQ NI6009 WISCO AL210 8AI+2AO, 14bit,48 ks/s 8AI, 24 bit, 1S/s 60,000 others Pick-Up Sensor Load-Cell Differential gear 30,000 5% 10% 46% Hydrostatic Equipment Torque Transducer Computer DAQ Electrical Parts 38% Figure 3 fraction of cost in this project 5

6 In case of imported dynamometer at same capacity, model # K, it is cost $44,950 or Bth1,612,000 [9] However, this is valid only in Thailand circumstance. CONCLUSIONS In this study, A 150 kw hydrostatic dynamometer has designed and studied feasibility for engine testing as low cost dynamometer. Furthermore, the equipments and components are acquired intentionally from local distributor and dealer due to availability in after sale services and maintenance. The total project cost is 3 times cheaper than commercial dynamometer at same capacity. However, the calibration equipments cost 38% of total project cost. The economic of scale in units building could share the calibration cost. ACKNOWLEDGEMENT This project has finance support partially from NSTDA, B4-1, Automotive for Sustainable Development Program and Sripathum University internal research grant fund for 2009 Formula TSAE. REFERENCES 1. Michael Plint and Anthony Martyr, Engine Testing: Theory and practice, Butterworth Heinemann, Oxford. 2. J.L. Lahti and J.J Moskwa, A Transient Hydrostatic Dynamometer for Testing Single-Cylinder Prototypes of Multi-Cylinder Engines, SAE Technical Paper , G.R. Babbit, et. al., Design of an Integrated Control and Data Acquisition System for a High-Bandwidth, Hydrostatic, Transient Engine Dynamometer, Proceedings of the 1997 American Control Conference, Vol. 2, 1997, p J.L. Lahti and J.J Moskwa, A Transient Hydrodynamic Dynamometer for Single Cylinder Engine Research, Proceding of 15th Triennial World Congress, Barcelona, Spain, G.R. Babbit and J.J Moskwa, Implementation Details and Teat Results for a Transient Engine Dynamometer and Hardware in the Loop Vehicle Model, Procedings of 1999 IEEE International Symposium on Computer Aided Control System Design, 1999, p Thitipatanapong, R., Development of Low- Cost Engine Dynamometor (in Thai), NECTEC Technical Journal, NECTEC- ACE2008 Special Edition, Vol. 8, Issue 20,,2008, p PUMP HANDBOOK, 3rd Edition, Ch3.8 Vane, Gear, Lope Pumps, McGraw-Hill, R.K., Mobley, Plant Engineer's handbook, Ch40 Hydraulic Fundamentals, CONTACT Raksit THITIPATANAPONG, Assistance Researcher, Embedded System Technology Research Laboratory, National Electronic & Computer Technology Center, 112 Phahon Yothin Rd., Klong 1, Klong Luang, Pathumthani 12120,Thailand, raksit.thitipatanapong@nectec.or.th Montien KAENSON, Lecturer, Automotive Engineering Department, Faculty of Engineering, Sripathum University, 61 Phaholyothin Rd., Jatujak, Bangkok, Thailand Sataporn KLYLUNG Lecturer, Automotive Engineering Department, Faculty of Engineering, Sripathum University, 61 Phaholyothin Rd., Jatujak, Bangkok, Thailand 6