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ENGINE TECHNOLOGY

A cutaway of the supercharger used on the Kawasak i 250X personal watercraft, along with a schematic of the engine system. Two air bypass valves balance air flo w upstream, downstream or wastegate air under variou s conditions of load and speed.

SUPERCHARGERS COMING

With engine efBACK INTficiency demands growing and new design concepts, superchargers are getting another looO FOCUS? k

BY ROB WILSON hen the subject is super ­ many ways, superchargers were jus t conditions of engine speed and loa d chargers, the knee­jerk re­ that — super. by two air bypass valves. sponse by motorheads far So perhaps it comes as no surpris e The Roots blower used in thi s and wide is “parasitic losses.” ThaW t that for the 2007 model year, Kawasaki application is produced by Ogur a simple phrase often puts considera­ is launching a high­performance per­ Clutch Co. in Japan, with U.S. head­ tion of superchargers to rest in th e sonal water craft (PWC) called the Ultra quarters of Ogura Industrial Corp. i n current era where emissions, effi­ 250X that derives some of its “hair o n Somerset, N.J. ciency and fuel economy are th e fire” capability through a supercharger . “The Kawasaki application is cer­ drivers for engine manufacturers . The Roots­blown, 1.5 L, inline four­ tainly high profile and Ogura is excited But new technology and more effi­ cylinder, intercooled gasoline engin e to be a part of it,” said Frank Flemming, cient designs seem to be promptin g produces 250 hp remarkable for a n president of Ogura Clutch Co. “Wit h another look. engine that size. That’s 166 hp per L , the 250X, the use of supercharging i s The Roots blower design on whic h which is nothing short of astonishing . strictly performance driven and th e many superchargers are based, actu­ Kawasaki claimed the 250X is th e results speak for themselves. ally predates the internal combustio n most powerful PWC in the world. Th e “High performance has also charac­ engine, and these devices were being supercharger produces large boos t terized most applications for super­ used to optimize blast furnace outpu t even at low rpm, the company said , charging but there is an evolution hap­ in the 1870s. Uses have abounde d and acceleration from idle is not ham­ pening where other factors are no w over time. pered by turbo lag. coming into play. And the supercharg­ Two­cycle diesels, of course, us e The blower for the 250X force­feeds er we are bringing to the market today them to scavenge exhaust gas. Fo r 2 L of air for every revolution, yieldin g has far more flexibility and capability. ” aggressive air handling in tight spaces, high­pressure intake air at all engin e Jim Ebisawa, engineering manager the reputation of Roots blowers wa s speeds and a flat, beefy torque curv e at Ogura Clutch Co., pointed out tha t never in dispute. over the operating range. Air pressure the Ogura TX series has adopte d The same can be said for high per­ is managed, balanced upstream o r Wankel rotary geometry design , formance and for power density. I n downstream or dumped under various which increases the working o r

XX DIESEL PROGRESS NORTH AMERICAN EDITION March 2007 March 2007 DIESEL PROGRESS NORTH AMERICAN EDITION XX DPNA295.qxp 2/23/07 2:38 PM Page 2

ENGINE TECHNOLOGY

ing on larger engines to optimize low­speed and high­speed per­ formance; • as an additional, fast acting, air­ Ogura has adopted Wankel­type geome­ handling device to help emissio n try to improve volumetric efficiency. The compliance, improve fuel economy twin counter­rotating rotors have a or both. cross­section shaped like a figure eight. Ogura has been working on devel­ The rotors are hollow from end to end for opment programs for diesel and gaso­ low inertia. line engines, mainly with engine dis­ placements smaller than 5 L, but a few upwards of 10 L. One program involves the KAD4 2 Volvo Penta marine diesel. Powere d by a turbocharged 3.6 L engine, th e sealed displacement of the pumpin g “There, the supercharger is driven al l boat simply couldn’t get up on plan e area and also improves volumetri c the time, but that need not be the case. due to low torque at low speed. Th e efficiency of the blower over the oper­ “For most of the pilot programs and addition of the Ogura supercharger to ating range. inquiries we are currently pursuing, a the 3.9 L diesel raised the torque a t Ebisawa said the TX volumetric effi­ clutch is certainly a big motivator o f 100 rpm by a factor of three and th e ciency advantage over other Root s the interest level. Almost all of ou r boat came up on plane. At 2500 rpm , blower designs can be more tha n superchargers have electric clutche s the turbocharger takes over and th e 20% at low speed and 10% on the top mounted on the front end and th e boat remained on plane. end. The design has fewer parts an d engine management system turns the Europe is described as somewha t is lightweight throughout its design. power on and off as needed. ” ahead in active development programs Twin counter­rotating rotors blow­ This capability is probably the rea l for supercharger application. There i s ing the air within the supercharge r game changer. When torque is not re­ also greater recognition in Europe tha t housing are hollow from end to end , quired, the supercharger is switche d supercharging has great potential fo r resulting in a very lightweight design , off in milliseconds and only a belt an d coming emissions hurdles. Better com­ reducing their moment of inertia an d idler pulley remain as parasitic losses , bustion on diesel engines at lowe r thus the energy required to mak e very small ones at that. At any rate, the speed is of particular interest. them rotate. drive belt is there driving other acces ­ And perhaps it can now be calle d The TX series superchargers ar e sories. When not required, the super­ adaptive supercharging. Why not ? designated by their theoretical dis­ charger is completely out of the circuit. The modus operandi is completel y charge per revolution. Thus the small­ To give an idea of response time , changed. Parasitic losses are no w est, the TX04, has a discharge vol­ engagement time is about 50 ms o n filtered out when the supercharge r ume of 0.4 L/rev, while the largest, the the smallest superchargers, on th e is disengaged. Now the supercharg­ TX28, has a discharge volume of 2. 8 largest about 50 ms. Disengagemen t er can bring a lot more air into pla y L/rev. The smallest weighs 11.6 lb . is 30 to 50 ms for all models . on demand without the traditiona l and the largest 31.3 lb. When torque is required, the en­ turbo lag. Maximum continuous speeds fo r gine management system cues th e Or maybe the requirement is fo r the TX series range from 9000 t o electromagnetic clutch to pick up th e more cool air to keep combustion tem­ 12,000 rpm and the maximum pres­ low inertia supercharger, producing a perature in the correct zone wher e sure ratio is given at 1.8:1. burst of power on demand. NOx generation remains under control. It happens that Ogura Industrial i s Where Flemming and Ebisawa se e For many compelling reasons, i t actually better known for its capabili­ the best fits are: seems the time for re­examination o f ties in clutches, but it has combine d • vehicles requiring high torque a t supercharger technology is at hand . this capability with the Wankel super­ low speed, with stop­and­go driv­ The potential is much changed. dp charger design, and this is wha t ing, hilly and poor road conditions; results in a completely new tool for en­ • wherever large engine perform­ For More Information gine aspiration. ance or burst power is require d NowNow On This Company Go To: “On the Kawasaki 250X jet ski appli­ from a small engine and wher e cation, the only interest is high per­ weight limitations might call for a DirectLink @ formance and so that unit does no t small engine; WWW.DIESELPROGRESS.COM incorporate a clutch,” said Flemming . • in combination with turbocharg­

XX DIESEL PROGRESS NORTH AMERICAN EDITION March 2007 March 2007 DIESEL PROGRESS NORTH AMERICAN EDITION XX