Lexus is renowned for its insistence on high quality, particularly in terms of build excellence.
From the first the marque was established, as a luxury arm of Toyota, it has also concentrated on pursuing that excellence in its engines, and second-hand Lexus V8s are much sought-after by modifiers who want great performance coupled with decent fuel economy.
However, unlike other engine makers, Lexus is not known for its innovative solutions, instead concentrating on building to ensure longer life, albeit at the expense of the out-and-out performance of its German premium competitors.
Turbochargers have been ignored, and specific outputs have not been particularly high – with the exception of the limited edition LF-A supercar Lexus developed in conjunction with Yamaha.
So it comes as a big surprise to learn that Lexus is turning all that on its head as it changes its tack, and starts a process which will see it going head-tohead against Audi, BMW, MercedesBenz and Volvo in the premium medium SUV market – and ultimately other segments – with the main weapon in its armoury a two-litre turbocharged engine that not only uses latest turbo technology, but also radically combines both Atkinson cycle and Otto cycle in one engine.
The new AR-FTS motor will make its debut in New Zealand in February next year in a petrol-only new model series on top of the recently-launched Lexus NX mid-size SUV range, swapping frugal Prius-like hybrid power for sub seven seconds 0-100km/h acceleration and huge turbodiesel-like torque of 350Nm on a massive plateau from 1,800rpm right through to 4,200rpm, with the maximum power of 175kW produced between 4,800rpm and 5,600rpm.
The engine, pursued at the doggedness of NX project chief engineer Takeagi Kato, who convinced his bosses Lexus needed it for the NX and other models in the Lexus lineup, has a capacity of 1,998cc, and is perfectly “square” for excellent revvability, with bore and stroke of 86mm.
Surprisingly, therefore, for a turbo engine, it runs with a massive ten to one compression ratio, and features a Lexusdeveloped twin-scroll turbocharger with an active waste-gate valve, designed to give quick throttle response with no lag.
The main solution to reducing turbo lag was to cast the four-into-two exhaust manifold integrally with the cylinder head, shortening the gas flow to the turbo to a minimum, and to have a liquid-cooled intercooler plus a variable waste gate for greater efficiency.
Part of the ability to being able to uses such high compression PLUS a pressure-boosting turbo, without blowing the engine to pieces, is in the capability of the engine to switch over from Atkinson cycle to Otto cycle, seamlessly, and without any discernible change in the engine note.
This eliminates pumping losses associated with purging the cylinders of exhaust gases and sucking in a new charge, while at the same time equalising internal and external pressures.
The Atkinson cycle is used at light loads; Otto at heavier loads.
The original Atkinson cycle engine was designed in the late 19th Century, and the first engine built in 1882, and its purpose was to avoid infringing patents on the Otto cycle engine.
Where it differed from the Otto was in allowing the intake, compression, power, and exhaust strokes of the fourstroke cycle to occur in a single turn of the crankshaft; however, it suffered from a lack of torque, and was quickly overrun by the German design.
Today’s so-called “Atkinson cycle” engines don’t in fact follow the original design, but are used to describe a modified Otto cycle petrol engine.
According to Wikipedia the modern Atkinson cycle describes an engine in which the intake valve is held open longer than normal to allow a reverse flow of intake air into the intake manifold.
The effective compression ratio is reduced (for a time the air is escaping the cylinder freely rather than being compressed), but the expansion ratio is unchanged. This means the compression ratio is smaller than the expansion ratio.
Heat gained from burning fuel increases the pressure, thereby forcing the piston to move, expanding the air volume beyond the volume when compression began. The goal of the modern Atkinson cycle is to allow the pressure in the combustion chamber at the end of the power stroke to be equal to atmospheric pressure, thus eliminating pumping losses, and all the available energy to be obtained from the combustion process.
For any given portion of air, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.
The disadvantage of the four-stroke Atkinson cycle engine versus the more common Otto cycle engine is reduced power density.
Due to a smaller portion of the compression stroke being devoted to compressing the intake air, an Atkinson cycle engine does not take in as much air as would a similarly designed and sized Otto cycle engine.
Lexus uses what it calls VVT-iW technology to achieve the switch from Atkinson to Otto, allowing the timing to be advanced or retarded as required, and moved from one cycle to the other as needed.
The new engine certainly has the power and torque to challenge some of the more-established players in the marketplace, and, with combined petrol consumption of 7.9L/100km on the NX 200t, should satisfy those who want their power and economy too.
Although the NX is the first car in the Lexus range to get it, I’ve been given the nod that this radical new engine will find its way into the CT range – currently hybrid only – as well as the bigger IS.
Can’t wait to drive ‘em!