VALVETRAINS

In the cam What’s next for valvetrain technology and cam-in-block applications in the land where pushrod designs rule? ETi travels to the USA to fi nd out

WORDS: MIKE MAGDA

ith much lower costs and continued improvements in materials and assembly, the market for concentric or single cam-phaser camshaft designs is likely to expand beyond cam-in-block applications, Wand this is especially true in the USA, where many engines are traditional single-cam, pushrod designs, which have well-known severe limitations in adapting VVT. In fact, the 8.4-liter V10 engine in the 2008 to 2010 Dodge Viper was the first US vehicle with concentric camshaft technology, originally developed by Mechadyne in the UK and supplied by Mahle Technology in Michigan.

The Dodge Viper was the fi rst vehicle in the USA to feature concentric camshaft technology 44 June 2011 Engine Technology International.com VALVETRAINS

45 Engine Technology International.com June 2011 VALVETRAINS

The Viper camshaft features a hollow camshaft tube 1 shaft to which cam lobes for the exhaust valves are fixed. A second, solid shaft is positioned inside the tube and drives the intake lobes, which are free to rotate on the outside of the tube. The timing gear rotates both shafts but a hydraulically actuated phaser – controlled by the ECU – can adjust the exhaust-valve timing up to 36° separate from the intake valves. Such flexibility enables engineers to specify an overall aggressive cam profile to achieve 600 peak horsepower at 6,100rpm, and then close the exhaust valves a little earlier at low rpm/light load conditions to help reduce high exhaust-gas dilution of the intake charge. “This [setup] enables a high-performance engine to behave itself at idle and low speeds, and with different kinds of engines you get different benefits,” explains Ron Pierik, senior engineer for advanced technologies at GM Powertrain, which designs a number of large-displacement pushrod V8 engines for full-size trucks, SUVs and performance vehicles. SCP technology on a DOHC engine, as an example, enables engineers to manipulate the intake valves individually in each cylinder to control the relative timing of each cylinder’s pair of valves. “When you split the event from one valve to the other, you can start doing some interesting things, including mixture motion and swirl,” says Pierik. “Or have one of 2 the valves close late to reduce pumping work inside the engine for fuel economy.” 1 and 2. An innovative “Attaching an actuator to the end of the camshaft that engineering solution Aside from increased power and better fuel economy, a from Mechadyne sees has two interfaces is more complex,” cautions Pierik. cam-in-cam solution offers other advantages, explains an integrated front cover As a result, suppliers are busy developing twin Wolfgang Rein, vice president of product engineering for feed that is ideal for a independent phaser designs, which could even be used on Mahle Technology: “With cam-in-cam, you can go to cam-in-block application a three-valve-per-cylinder engine design. “We find that different combustion systems such as the Miller Cycle or every customer has a unique set of design criteria,” says derivatives of it. The idea is to go to dual phasers, then Dr Tim Lancefield, technology director at Mechadyne. this degree of freedom will increase.” “The challenges vary from project to project.” Current single phasers allow only the camshaft tube Two independent phasers usually require four oil feed/ timing to change relative to the crankshaft. However, dual return lines, but Mechadyne’s solution is an integrated phasers enable engineers to adjust the timing of both sets front cover feed that is ideal for a cam-in-block application. of cam lobes relative to the crankshaft, and independently The company has also developed an integrated twin-spool of each other. valve that requires only a single oil feed.

Mike Magda, Dean Slavnich, international freelancer editor, ETi For me it’s the 1994 Mercedes-Benz 500 Okay, so it might not be the most exciting – developed and built by Ilmor for Penske valvetrain setup, but Fiat’s MultiAir (or UniAir as Racing. I’ve chosen this not just for the clever Schaeffl er terms it) represents a decade of hard and top-secret arrangement of inclined valves, work for these two partners. The cam-actuated long-ratio roller rockers, and short-pushrods electrohydraulic valvetrain implements throttle- that cleared the huge inlet ports, but also for free continuously variable software-based load the unique fi nger-type followers control across the entire engine map. The long mounted on a shaft parallel and short of it is that, for the fi rst time, a fully to the camshaft – instead of variable valve-control system has conventional lifters – that come on the market that enables not only reduced friction but multiple opening and closing of increased valve lift. valves at different intervals of the cycle, as well as variations in valve lift. All this means huge inroads in slashing emissions and improving fuel economy, as well as no fewer than fi ve International Engine of the Year Awards in two years! THE WORLD’S GREATEST VALVETRAINS

46 June 2011 Engine Technology International.com VALVETRAINS

“When you split the event from one valve to the other, you can start doing some interesting things, including mixture motion and swirl”

3 4

3 and 4. The Viper V10 – “Cross-talk and oil consumption can be problematic assembly process, but maintaining precise tolerances is with a hollow camshaft with some twin-phaser designs,” continues Lancefield. critical. “It is very easy to design and make a concentric tube shaft to which cam lobes for the exhaust “We’ve done a lot of development on the oil feed paths camshaft that is internally over-constrained,” warns valves are fi xed – was within the twin phaser, resulting in very good leakage test Lancefield. “If the holes in the inner shaft and moving ahead of its time in the USA results that are either on par with, or better than, current lobes are only slightly out of position, there is a tendency production single phasers.” for such a camshaft to lock up during assembly as the As research continues, OEMs identify challenges and various pins, fits, and holes all fight each other. concerns in adapting cam-in-cam technology. Internal “It is important not to distort the driveshaft during the friction losses and binding are possibilities, as is the pinning operation otherwise this too can result in higher durability of the cam assembly and grinding the lobes. friction levels.” The same materials and heat treatments found in One solution turns the pins into a mechanism that is conventional assembled shafts are used in concentric similar to the Oldham coupling that results in barely camshafts. However, differences will depend on the measurable friction levels, even when the camshaft is

Ian Methley, technical Graham Johnson, managing Dr Kurt Kirsten, CTO, specialist, Mechadyne director, UKIP Media & Events, Schae er Group International publisher of ETI The answer to this My favorite valvetrain must be Greatest valvetrain of all time? Easy: Honda’s is time dependent. the Honda VTEC because it mechanical VTEC system. A system so complex The fi rst really emphatically demonstrated how that it actually jumped onto a different cam clever valvetrains VVA can transform engine profi le as the revs climbed, yet folklore has it were the phasers, performance. Introduced that Honda never had a single warranty claim and the camshaft when humble phasing on the system. And here’s the thing: it was just phaser system was systems were still a rarity, fl aming fantastic to experience! The intoxicating very smart. Then the VTEC led the VVA market noise; the tremendous extra push as it phaser system and variable for over 10 years until reached that little bit of valvetrain heaven; valvetrain were combined by BMW continuously variable lift the fuel economy/performance balance it and Honda – and these were very systems became available, enabled; complexity that was made to feel good. Then there were sophisticated so you have to applaud so seamless; and 9,000rpm! Today, Honda systems from Audi and Porsche, and Honda’s vision. gives us iVTEC, a dull electronic system by now it’s the turn of UniAir. All these comparison that doesn’t deserve to wear systems were important, but perhaps the letters V-T-E-C on its cam covers. when you take time into account, the Still, it could be worse. After all, Honda BMW/Honda technology opened is also the OEM that gave us IMA! the door the most.

47 Engine Technology International.com June 2011 VALVETRAINS

1 Q&A Dr Kurt Kirsten, CTO, Schaeffl er Group

Does the UniAir/MultiAir technology represent a new, higher benchmark in valvetrain optimization? Let me start by saying there’s no silver bullet when it comes to valvetrains. There’s no right way, and it really is all about diversity. Each system is the right system and has the right to perform. Now, is UniAir the most capable system on the market? Well, it certainly has the highest degree of freedom. It has some major advantages because you can control it cycle-by-cycle and valve-by-valve. At this stage, Fiat’s MultiAir System has the highest degree of freedom and because of that, it has opened the industry’s eyes.

A decade ago Schae er and Fiat started working on UniAir/MultiAir, and today, this system has been widely praised and accepted by the market. What’s next for this technology? First, the technology needs to stabilize itself on the market. The fi rst generation of MultiAir/UniAir has been a tremendous success, but the next step will be generation two and this will be an enabler for further combustion improvement. The second generation is due next year.

Will UniAir open the door to fully electrohydraulic powertrains? installed in a cam bore slightly out of line. “In a perfect 1. Many see the i-VTEC as There are a couple of players in this area, namely BMW and world, grinding would take place with the lobes on the an unworthy successor to PSA with the valvetronic system developed by BMW. The Honda’s screaming VTEC cam,” says GM’s Pierik. question is, will they go fully electrohydraulic? Is it worth it for them to make this switch? On a cost basis, no, the switch Lancefield further explains: “The choice to grind the 2 and 3. Co-developed is not worth it, and from a marketing approach, there might lobes off or on the camshaft fundamentally comes down with Schaeffl er, Fiat’s MultiAir technology points be no value added to the system either. There are many to the cam assembly process. Those resulting in minimal to a new era in valvetrain different roads to Rome and the UniAir/MultiAir technology lobe-tube distortion, such as shrink-fit, where the management solutions is just one option. camshaft tube is cooled in liquid nitrogen, then passed through a fixture containing the cam lobes, are able to use Are you worried about the so-called finish-ground or net-shape cam lobes. But other processes electric powertrain revolution? such as mandrel expansion or knurling of the tube may I am confi dent that the IC engine will remain at least until require grinding after the assembly.” the end of my career – if not longer – and I’m 15 years Mechadyne reduces the chance of grinding dust away from retirement! contaminating the moving surfaces by coating the cam in wax, prior to grinding or feeding coolant inside the Will the USA continue to opt for camshaft during the grinding process. The former is for traditional single-cam pushrod designs? use in low-volume production while the latter is used for The cheapest way to realize certain power and torque levels is cubic inches and this explains the single-cam systems they use. Now, though, CAFE standards are 2 leading those in the USA to turbochargers, downspeeding and downsizing. As a result, there are going to be big changes in the USA and I think it will follow Europe in terms of trends and technologies.

high-volume. “There is a cost balance between part-level costs and the assembly-process cost,” says Lancefield. “Grinding lobes before assembly may be a more cost- effective solution at a component level but a more costly assembly process may be required to ensure profile positioning accuracy and minimal distortion after assembly.” With such inroads being made in the development of production processes, combined with the relentless quest to further improve fuel economy and performance, the use of concentric camshafts may no longer be confined to 3 niche products, such as the Viper. 48 June 2011 Engine Technology International.com