Pneumatic re-generation system in an electric car Ziming Qi, Vivien iang & David Hawkins Abstract As the clean energy car becomes the hot sot on the market, the electric car has been aid more attention. Although the weakness of the battery has recently been overcome (e.g. it has shorter charging time, higher ower density, and longer life), in the current hybrid car, one more asect concerned is efficiency. Efficiency of transformation from the energy of motion to electric energy is much lower than that from one tye of mechanical energy to another tye of mechanical energy. his aer is to resent a novel design of neumatic re-generation system hybrid in an electric car. First of all, in order to increase life of the battery, the battery isn t recharged during the car is running. It s only charged by the main ower in the garage - It is called lug-in electric car. Secondly, the energy from the car s deceleration will be catured by a secial gear box and be stored in the comressed air tanks. hirdly, the energy stored will drive an air motor to suly sulemental ower. Since this chain is a mechanical energy transformation, in theory, efficiency is higher than tyical hybrid car. he exeriment seems to get a satisfy result. A eywords electric car; hybrid car; comressed air I. INRODUION n electric car has been aid an attention as its secification shows an accetable to seed, a range of more than 60km (00 miles) on a full charge and a resealable rice e.g. Nissan EAF[]. However, a question is still needed to be answered: Is it available for an urgent recharge when it shos on a bridge with a flat battery? urrently an ure electric car cannot have a satisfy answer since it is only able to offer a quick charger that can charge u to 80% of its full caacity in just under 30 minutes and charging at home through a 00V outlet is estimated to take aroximately 8 hours. herefore, some researches had suggested an office facility, equied with renewable energy sources, where the users can recharge their lug-in electric vehicles, using the available renewable ower []. Unfortunately such a facility does not offer an on-road solution, a hybrid car with an electric motor and an internal combustion engine (IE) is still a consideration to reduce the oortunity of the issue of a flat battery on road. As such a hybrid car still need an IE, which is a main concerned for its emission, a regenerative braking is an alternative solution. A regenerative braking is to reduce the fuel consumtion. Whilst most existing regenerative braking systems in a car transfer energy with generators and motors using batteries, an Z. Qi is with Unitec Institute of echnology, Auckland, New Zealand. (e-mail: tqi@unitec.ac.nz) V. iang is with ubic Defence New Zealand, Auckland, New Zealand. (e-mail: vivien.liang@cubic.com) D. Hawkins is with Unitec Institute of echnology, Auckland, New Zealand. (e-mail: dhawkins@unitec.ac.nz) 4 alternative regenerative braking system using a hydraulic drive with comressed air or nitrogen was dislayed for a Ford onka ruck [3]. A reort showed this regenerative braking system had fuel savings during sto and go traffic u to 35% and reuse 80% of the braking energy. However, such a regenerative braking system cannot be commercialised in assenger s cars as it is not cost efficiency. It had to ensure the safety since a very high ressure is alied in this system. his aer is to resent a novel design of neumatic re-generation system hybrid in an electric car. First of all, in order to increase life of the battery, the battery isn t recharged during the car is running. It s only charged by the main ower in the garage - It is called lug-in electric car. Secondly, the energy from the car s deceleration will be catured by a secial gear box and be stored in the comressed air tanks. hirdly, the energy stored will drive an air motor to suly sulemental ower. Since this chain is a mechanical energy transformation, in theory, efficiency is higher than tyical hybrid car. Since the maximum working ressure is 0si or 8bar, the cost for commercialised is at minimum level. II. DESIGN MEHOD he figure shows a hyothetical indicator diagram for the comressor. Figure hyothetical indicator diagram for the comressor As shown in Figure, from situation a to, the air is drawn into the cylinder on the suction stroke. From to, the suction valve is closed and air is comressed according to the law Pv n c () From to b, the delivery valve oens and air is delivered under ressure. From b to a, the delivery valve closes and the suction valve oens.
he figure shows the structure for the air ower system. Figure the designed system As shown in Figure, the cloud callout shows the same rocess with the hyothetical indicator diagram for the comressor. Assumtions in the system shown as Figure :. Steady oerating conditions exist;. kinetic and otential energy changes are negligible; 3. he rocess is given to be adiabatic (transfer of heat across the system boundary) Ideal gas the equation of state: Adiabatic rocess PV Rm () v k constant (3) Where k is Ratio c / c v k.4, when it is, H, O, O, NO, or H. k.3, when it is O, SO, H O, H S, N O, H S ( V V V V ) ( V ) W V [( ) ] (6) V ( ) ε (7) When the golf cart goes downhill, the ower is switched off, and the air comressor is turned on and is driven by the running gear. he work done on the air er cycle is W V [( ) ] (8) In this eriod, the work done on the cart by the friction is W f F cosθ S (9) Where is Fiction coefficient, F is Weight of the cart, θ is Degree of the hill, S is the distance the cart runs. omaring these two works, we can get the efficiency of the transmission. III. EXPERIMENS A tyical electric golf cart has an electric motor and a battery. It is not only used in golf courts but also many worklaces e.g. railway stations and airorts. A tyical golf cart lub car is emloyed in this roject as showed in Figure 3. eeing the existing electric motor and battery (also all other equiment) in golf cart so that it can be oerated as usual, this golf cart was Installed an air comressor and an air motor. A gear box in a golf cart was designed to enable additional ower that can be transmitted or received from/to the axis in a golf cart. A clutch to switch the gearbox drive to an air comressor to store energy from the axis or switch the gearbox drive to an air motor to release energy to the axis. Figure 4 shows an overview of a modified golf cart. he system assemble is located at rear art. hus: v v k (3) v v k k k (3) (4) (5) he theoretical work done on the air er cycle is the area enclosed by [ a---b- a ] which equals V V W dv dv ( V V ) V V V Figure 3 overview - the system assemble at the rear art of the golf cart 5
As showed in Figure 5, there are 4 major arts in the comressor air system: A comressor tank, a clutch with belt, an air comressor and an air motor.. Fully ower the cart by electric motor then turn off the ower to let it free running;. Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air comressor; 3. Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air motor. 4. Power the cart by air motor from still condition. he main oints of the exeriment:. Every time, from the same osition A to fully ower the cart by electric motor ; Every time, at the same osition to turn off the electric motor and at the same time to switch on the air comressor or air motor. Figure 4 the comressed air system he air comressor (as in Figure 5) is to regenerate the energy of motion (when the golf cart is at downhill or shoing). he comressed air tank is to store energy from the motion of the golf cart. An air motor is to outut the stored energy in the comressed air tank via the belt to the gear box to rovide an additional assistant to the electric motor when it is needed. he regenerative rate (RG) can be calculated Where RG inut u (0) outut / P / P down inut is the travel distance of golf cart lost, which is caused by the tank receiving comressed air. outut is the travel distance of the golf cart using the comressed air from the tank. P is the level of arising ressure in PSI, which means u receiving energy to the tank. P down is the level of falling ressure in PSI, which means oututting energy from the tank. A. Road condition : here is a curve in a gentle downhill (in 5 ).as shown in Figure 9. Figure 6 there are a curve in a downhill Figure 5 Power transmitting unit ondition of the exeriment:. Golf cart: Electric motor: 4kw, 48 volt; Max seed: 35km/h Net weight: 30 kg. comressor: 3. tank: 50 litres 4. motor: Procedure of the exeriment: Procedure : Fully ower the cart by electric motor then turn off the ower to let it free running. oint is 40 meters. Procedure : Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air comressor. he results are as able. It means the tank receives the motion energy of average of 0 meters by increasing 4 PSI in ressure. Procedure 3: Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air motor. he results are as able. It means that the golf cart moves 0 meters over 40 meters sends average of 0 PSI in ressure. 6
able 3 4 5 able ressure at oint ressure at oint 56si 60si 0 metres 59si 63si 0metres 6si 66si 9metres 64si 69si 9metres 68si 7si 9metres ressure at oint ressure at oint 68si 58si 50 metres 74si 63si 5metres Procedure 4: Power the cart by air motor from still condition. he results are as able 3. It means that the comressed air drove the golf cart meters by sending PSI in this test. able 3 ressure at oint ressure at oint 64si 53si 6 metres 5si 33si 3metres omaring able and, there is a regenerative rate is 80%.. Road condition : he test was in a flat oen road with a gentle uhill (less than 5 ). able 4 ressure at oint ressure at oint 5si 5si 5metres 60si 6si 7.8metres 3 60si 6si 6.5metres 4 6si 6si 6.6metres 5 6si 64si 6.4metres 6 64si 64si 6.metres 7 64si 64si 6.metres 8 64si 65si 6.metres 9 65si 66si 6.metres 0 66si 67si 6.metres 67si 68si 6.metres 68si 69si 5.8metres 3 69si 69.5si 6metres 4 69.5si 70si 6.metres 5 70si 70si 6.metres Procedure 3: Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air motor. he results are showed as able 5. It means that the golf cart moves 6 meters over meters sends average of 0 PSI in ressure. able 5 ressure at oint ressure at oint and 60si 49si 8 metres ressure at oint after sto a while 70si 54si 5.7 metres 57si 38si 03si 4.3metres 06si Figure 7 est in uhill Procedure : Fully ower the cart by electric motor then turn off the ower to let it free running. he distance oint is meters. Procedure : Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air comressor. he results are as able 4. It means the tank receives the motion energy of average of 6 meters by increasing PSI in ressure. omaring able 4 and 5, there is a regenerative rate is 5%. As the road condition is not flat and uhill, an extra rocedure was arranged: Reeat rocedure : Fully ower the cart by electric motor then turn off the ower to let it free running. oint is. meters and the distance oint and is9 meters. It means from to is uhill. Reeat rocedure : Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air comressor. As showed in able 6, when it is uhill, the tank receives the motion energy of average of 6 meters by increasing PSI in ressure; when it is downhill, the tank receives the motion energy of average of 9 meters by increasing PSI in ressure. 7
able 6 ressure at oint Go from to ressure at oint ressure at oint Go from to ressure at oint and 50si 50si 7 46si 49si 9.9 49si 5si 5.9 5si 53si 8.6 3 53si 54si 7 54si 55si 7.5 4 55si 56si 6. 56si 57si 9 Reeat rocedure 3: Fully ower the cart by electric motor then turn off the ower, at the same time switch on the air motor. he results are showed as able 7. When it is uhill, the golf cart moves 6 meters more over meters sends average of 4 PSI in ressure. When it is downhill, the golf cart moves 0 meters more over 9 meters sends average of 8 PSI in ressure. omaring able 6 and 7, when it is u hill, there is a regenerative rate is 7%. And when it is u hill, there is a regenerative rate is %. able 7 ressuer at oint Go from to ressure at oint ressuer at oint Go from to ressure at oint and 69si 55si 6. 70si 5si 9.5 70si 56si 6. 70si 5si 9. Road condition 3: A new road condition as shown in Figure 8, fully ower the cart by electric motor then turn off the ower, at the same time switch on the air motor. he results are showed as able 8. When it is uhill, the golf cart moves 6 meters sending average of 0 PSI in ressure; when it is downhill, the golf cart moves 7 meters sending average of 8 PSI in ressure. he test started at 0:54 last Monday. ressure increased from 0 to 00si in minutes. emerature changed from 9deg to 44deg. When the ressure droed to 50si, temerature was 38deg. When the ressure was 50si, we started the motor to drive the comressor to increase air ressure to 60si then 70si, the relevant temerature was 34deg, 38deg and 44deg. We reeated the same exeriment for other three times: the air ressure increased from 50si to 70si, the relevant temerature changed from 3deg to 44deg; 39deg to 48deg and 39deg and 48deg. oncluding from the records, when the air ressure increased from 50si to 70si, the temerature difference is about 9~0deg. IV. ONUSION AND DISUSSION his research had confirmed that the comressed air in an electric car is suitable for regenerating energy from motion and being used as additional ower source. Additional finding is that the regenerative rate can be 5%-% in a normal road condition. While it is in downhill, the regenerative rate reaches as much as 80%. REFERENES [] "Nissan unveils "eaf" electric car." vol. 009: hannel NewsAsia, 009. [] J. F. Martins, V. Fernao Pires,. Gomes, and O. P. Dias, "Plug-in electric vehicles integration with renewable energy building facility - building/vehicle interface," in Power Engineering, Energy and Electrical Drives, 009. POWERENG '09. International onference on, 009,. 0-05. [3] F. Wicks, J. Maleszweski,. Wright, and J. Zarybnicky, "Analysis of comressed air regenerative braking and a thermally enhanced otion," in Energy onversion Engineering onference, 00. IEE '0. 00 37th Intersociety, 00,. 406-4. Figure 8 Procedure 3: able 8 ressure at oint Go from to ressure at oint ressure at oint Go from to ressure at oint and 70si 50si 4.9 70si 5si 7 70si 50si 7 70si 5si 6 3 70si 5si 8 70si 5si 8 8