PERFORMANCE AND DESIGN ANALYSIS OF REGENERATIVE BRAKING SYSTEM

Transcription

1 PERFORMANCE AND DESIGN ANALYSIS OF REGENERATIVE BRAKING SYSTEM Dr. Deo Raj Tiwari 1, Vinod Kumar 2 1,2 Associate Professor, IIMT College of Engineering Greater Noida, (India) ABSTRACT A vehicle supported for rolling movement on a track by a first set of wheels driven by an electric motor and a second empowered set of wheels is provided with an improved braking system. The braking system includes a brake pedal which can be depressed to generate a brake demand signal, a regenerative braking system associated with the electric motor and a friction braking system attached to the empowered wheels. Control circuit, which regulates the operation of the two brake systems, serves normally to actuate the regenerative braking system in response to the brake demand signal and to actuate the friction braking system only when the brake demand signal exceeds a predetermined level which corresponds normally to the maximum regenerative braking available. Under slippery rail conditions, a detector indicates slippage of the wheels relative to the rails during regenerative braking and immediately actuates the friction braking system to produce additional braking in proportion. Keywords: Regenerative Braking, Hybrid Vehicle, Power train, RESS I. THEORY Regenerative braking is a method to capture and store the kinetic energy of a moving item, and then be used to reaccelerate it. Regenerative braking is not industry specific, but can be difficult to implement cost effectively 1. In most application a heavy load must be stopped and started frequently. The action of starting and stopping is controlled to limit power required. In Industrial applications, the acceleration time and the deceleration time is usually easy to determine and microprocessor controlled 2. In an automotive drive train application, the braking energy will be much greater than the accelerating energy for a much shorter time. Electric regenerative braking in industrial applications is not known for being efficient. Generating and storing energy over a wide rpm and torque range is difficult. All systems have an operating voltage. When a generator rpm varies, so does the voltage output. The amperage varies with load. All the variable speed control electronic systems that have been looked at are not averaging over 80% efficiency driving a varying load over their operating speed range. No data has been found on the efficiency of any regenerative system. Some of the new systems are using power electronics, but the cost and efficiency has not proven to offset the cost of prop pitch control 3. The most common application for hydraulic regenerative braking is in hydraulic elevators. Most have a hydraulic cylinder to raise the car, when letting the load down the flow pressure is diverted to accumulators. Hydraulic hybrid drives currently being developed use a swash plate pump/motor and valves to divert the flow and pressure to accumulators. Neither of these systems have great efficiencies based on the calculations. 419 P a g e

2 One of the greatest challenges in regenerative braking is converting low energy inputs to a higher energy level required for peek acceleration power. For these reasons current electric or hydraulic hybrids cannot be considered as long term winners in saving energy. In theory if all the kinetic energy could be captured and reused for reacceleration, the only power required for a vehicle is to overcome wind, rolling resistance and climbing hills. II. HYBRID VEHICLE A hybrid vehicle (HV) is a vehicle that uses two or more distinct power or fuel sources such as An on-board rechargeable energy storage system (RESS) and a fueled power source for vehicle propulsion: (1) Internal Combustion Engine (2) Transmission (3) Electric motor (4) Power Electronics system (5) Fuel tank (6) Battery pack Hybrid electric vehicles are a combination of an internal combustion engine (1) and a battery and electric motor (3) of an electric vehicle. In current hybrids, both the engine (1) and the electric motor (3) are connected to the wheels by the same transmission (2) Intelligent power electronics (4) is a device that decides when to use the motor or internal combustion engine and when to store regenerated electricity in the battery (6) for future use. In a hybrid, when the brakes are applied, the motor becomes a generator. This generator uses the kinetic energy of the vehicle to generate electricity. The electricity is stored in the battery for later use. A simple way to think of a hybrid is to think of a moped. There is a gas powered engine and the second form of energy is your foot. Imagine if, instead of using your foot every time you needed to kick the ground, you could take the kinetic energy your body makes by pulling your foot up or setting it down, and storing it in the board. That would be similar to what the battery/engine hybrid does for a vehicle. Unlike all-electric vehicles, hybrid vehicles do not need to be plugged into an external source of electricity. Gasoline stored in a conventional fuel tank (5) provides all the energy the hybrid vehicle needs. 420 P a g e

3 III. PROBLEM STATEMENT Need arises for regenerative braking system is due to drawback in conventional friction based brake. We know that, the conventional friction based brake, however, is 0% efficient in terms of recovering the kinetic energy lost in deceleration. By using regenerative brake, this efficiency reaches 30% of electric generation. Another drawback of vehicle is starting problem in cold season. To reduce this drawback, we can use electrical energy from battery of R.B.S. and rotate main shaft of the engine easily. For three decades now, the second commandment of every automotive engineer right behind reducing cost has been to reduce fuel consumption and finding the alternative of fossil fuels. The drive to use less fossil fuel has dictated the design of engines, transmissions and control systems for decades. Now, it is pushing the development of completely different technologies for generating power. In spite of all these improvements, the energy efficiency of the most modern production car is still less than 20 percent. Most of the energy used to move the vehicle at any speed over any distance is thrown away as heat. About half of that wasted energy goes through the brakes. Today, almost every manufacturer is developing ways to recover a significant portion of that wasted energy with regenerative brake. While the technology itself is often complex, the concept is quite simple: Brakes slow and stop a car by converting kinetic energy, the energy of motion into heat energy, which is then dissipated to the air. We burn fuel to make heat and put kinetic energy into the car, and then we throw that energy away as waste heat. The goal of regenerative brake is to recover some of that energy, store it and then use it to put the car into motion again. It is estimated that regenerative brake can eventually be developed to recover about half the energy we now waste as braking heat. Depending on the type of vehicle, this would reduce fuel consumption by 10 to 25 percent below current levels. IV. DESIGN ANALYSIS: 4.1 Design of Shaft: Shaft is designed on the basis of consideration that shaft is subjected to combined twisting moment and bending moment. 421 P a g e

4 Let τ = Shear stress T = twisting moment M = bending moment Te = equivalent twisting moment Te = (M 2 +T 2 ), According to maximum shear stress theory, the maximum shear stress in the shaft, load on the Shaft =3.5x9.8=34.3N, Length of the Shaft =90.0 Maximum Bending Moment = N-mm. P = 2xπNxT/ 60= 2x3.14x250xT/60 =.5x1000 T =23885 N-mm Te = (M 2 +T 2 ) = ( ) = Te = (3.14/16) xτxd 3 d =14.5mm Therefore desired diameter of shaft is 16mm. Total 4.2 Design of belt: ( T1/T2) =e (µxθxcosecβ) Sin(α) =(r2/r1)/x =(100-50)/(2x60) α =24.60deg Angle of lap( θ)= 180-2α = 180-2x24.6 θ = 130 deg=2.268rad. Groove Angle =30 deg. T1=e (.3x2.268x2) T2 =3.9T2 T1-T2=955.4 T1 = T2 = x3.14xN2 (T1-T2) x(100/2) =.5x1000x1000 N2 =100rpm, Length of belt, L =3.14x (r2-r1) +2X + ((r2-r1)/x) 2 = 1.435mm 4.3 D.C. Motor Capacity : 12V RPM : 200 Wheel Dia: 50mm 4.4 Stepper Motor Output : 6V RPM : 125 Base plate : 660x360x25mm 3 Shaft : 16mm Dia., Length-900mm Motor wheel : 50 mm Dia. Pulley : 100mm Dia. Main Wheel : 400mm Dia. Brake Wheel : 220mm Dia. Gen.Wheel : 80mm Dia. Spring (K) : 50N/m 422 P a g e

5 PICTURES OF MODEL AND PARTS V. EXPERIMENTAL RESULT OF MODEL: Output voltage ranges from 5.5 to 6.0 volt Output current ranges from 90 to 100 ma Time taken to full stop from maximum speed to zero is 28 to 40 second Average output voltage (V) = ( ) / 2= 5.75 V Average output current (I) = (90+100) / 2 = 95 ma Average time taken to full stop (t) = ( ) / 2=34 sec Electrical energy stored (E) = V * (I i - I f ) / 2 * t = 5.75 * (95 0) / 2 * 10* 34 (I f = 0 and 1 ma =10-3 A)= 9.23 J Mass of one wheel (M) =1250 gm = kg Radius of wheel (R) = 200 mm= 0.2 m Maximum Average speed (N) = 325 rpm Speed ranges, before braking, from 300 to 350 rpm Angular velocity (ω) = 2πN/ 60=34 rad / sec Moment of inertia of two wheel = 2* MR 2 (taking wheel as a ring ) = 2*1.250*0.2 2 = 0.1 kg/ m 2 Rotational kinetic energy (K) = ½ I ω 2 = ½ 0.1 * 34 2 = J 423 P a g e

6 Braking efficiency (η) = Electrical energy stored / Initial rotational kinetic energy = 9.23 / =.1596J => η = % VI. CONCLUSION Regenerative Braking System is used in the Hybrid Car. This system is a method to capture & store the kinetic energy of a moving item, & then be used to reaccelerate it. In vehicle we apply the paddle brakes dually fitted with gear assembly and an AC generator to produce electrical energy with a small wheel. This wheel, when come into contact with main shaft, moves and rotates the gear assembly to provide a reassemble torque to run an AC generator for mechanical to electrical energy production. The electrical energy is than converted to ripple DC to provide charging voltage to 6V chargeable battery. Further this battery can be utilized to run fan/bulb or to provide initial torque to vehicle. VII. SCOPE FOR FUTURE WORK The Civic Hybrid uses the standard transmission behind the engine configuration. Because the Integrated Starter/Alternator provides regenerative brake, the transmission handles both positive and negative power delivery. The ultra thin, brushless DC motor is installed between the engine (below, in red) and the transmission. Honda figured out how to make the motor smaller by winding the poles asymmetrically, achieving 27 percent greater space efficiency. The closer poles not only reduce the size of the motor, but also improve torque. Regenerative brake can be extremely powerful. According to Craig Van Battenberg who teaches Honda and Toyota hybrid service at Automotive Career Development Center in Worcester, MA, no more than 17 percent of its capability is used in these cars to avoid putting people into the windshield. Even at that low level of use, in a typical mixture of highway and around-town driving regenerative brake can recover about 20 percent of the energy normally wasted as brake heat. This reduces the drawdown of the battery charge, extends the overall life of the battery pack and reduces fuel consumption. Right now, the Honda Insight, Toyota Prius and Honda Civic hybrid are the only production cars that use regenerative brake. However, regenerative brake has been used in trains, elevators and other industrial equipment for almost a century, and it will likely be used on many more cars and light trucks in the next decade. The technologies for recovering kinetic energy vary greatly, and some ideas are more promising than others. Here s a look at what s being seriously developed for automotive use. 424 P a g e

7 Now days, one of the leading automobile company General Motors is using this concept in their hybrid vehicle. This is used as storage of electric energy in battery.the concept is used by General Motor through using two electric motor A & B.Battery is connected to engine control unit. Energy control unit are connected to two electric motors that are used to drive two output shafts. Regenerative braking system will be highly used by most of automobile company for fuel alternative. Many problem such as starting of engine, driving on hill station, lighting system, fans,air conditioning are regulate through this concept. The efficiency of system will enhance by regenerative braking system. VIII. LIMITATIONS OF THE SYSTEM Traditional friction-based braking is still used with electrical regenerative braking for the following reasons: The regenerative braking effect rapidly reduces at lower speed; therefore the friction brake is still required in order to bring the vehicle to a complete halt. The friction brake is a necessary back-up in the event of failure of the regenerative brake. The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power or if the battery or capacitors are already charged. For this reason, it becomes essential to incorporate dynamic braking also for absorbing the excess energy. REFERENCES [1] Crouse W. H., Automotive engines, McGraw Hill International, 8 th edition,1995. [2] Singh Kirpal Automobile Engineering,Vol.2,(page.30) [3] Ganeshan V. Internal Combustion Engines, 4 th edition, paperback-16, Apr [4} Cleg S. J. A review of Regenerative Braking Systems, Working paper-471(1996), Institute of Transport Studies, University of Leeds, U. K. [5] Discussion on the Regenerative Braking of Electric Vehicles (Hellmund), Pittsburg PA, Transaction of the American Institute of Electrical Engineers 36, p68, Retrieved 11 March, P a g e