While even mainstream European truck manufacturers were pushing ‘alternative’ power to the forefront at the IAA, the industry’s Tier One and Two suppliers were finding ways of squeezing the last drop of efficiency out of diesel.
With the industry agreeing to new efficiency targets for heavy-duty diesels, there was obviously a great incentive to introduce new technology for what might be the last hurrah for the diesel truck… or, maybe not.
Two main approaches were evident: one being to reduce internal losses in the engine and the other to recover energy that would otherwise be wasted, whether that be from the exhaust flow or by using regenerative braking.
Cylinder deactivation is a radical step. Jacobs can utilise its famous ‘Jake Brake’ compression braking technology and hardware to deactivate cylinders when an engine is operating in low-load conditions. With no fuel injection or pumping losses there is an obvious fuel saving, an added bonus is that, as the remaining cylinders are working hard, exhaust gas temperature, and thus the efficacy of exhaust aftertreatment systems, is maintained. Typically, on a six-cylinder engine, three cylinders can be deactivated. Jacobs is working with engine makers in Europe and North America on the technology’s introduction.
The company has also developed a variable valve-opening system, for inlet and exhaust valves. It enables engine designers to vary compression ratio according to load and requirements, improve turbocharger response, and maintain exhaust stream heat. Its ability to reduce cylinder scavenge on demand has the potential to replace or at least reduce external exhaust gas recirculation systems and their attendant packaging and cooling issues.
Mahle also offers a variable valve-timing system – again citing its ability to offer engine designers the facility to boost engine braking, maintain exhaust temperatures or vary compression ratios.
Waste exhaust heat can be harvested by Mahle’s e-Waste Heat Recovery System. This extracts heat from the exhaust flow and converts it to 48v electricity that can either be used to power electrified accessories, removing parasitic drag, or return energy directly to the crankshaft. Fuel savings of around five per cent are claimed for the so-called Boost Box, giving a payback of around two years, and the device can even be retrofitted to vehicles in service.
Federal-Mogul was promoting a wide range of hybridisation strategies – which did not necessarily mean driving wheels electrically, but rather using electrics to optimise fuel consumption and to store energy. In smaller trucks, for instance, energy recovered could be used to drive an electric supercharger in place of a turbocharger, giving a downsized four-cylinder engine the response of a larger six, while saving fuel and weight.
Current engines put about one-third of their energy output out of the exhaust, and although much of this can be recovered by the turbocharger, when the turbocharger itself is not used to boost engine power then that energy could be recovered electrically and returned to the vehicle battery.
Regenerative braking, where ‘electric machines’ or motor-generators are placed in the drivetrain, can facilitate engine stop/start, and will give an immediate fuel saving if the energy recovered is used to help propel the vehicle.
If a second clutch is added, this enables the main engine to shut down when the vehicle is moving. A possible application is to use the diesel engine to accelerate the truck to around 50 km/h, then shut down and allow the electric machine alone to maintain vehicle speed while power reserves allow.
Whatever solution is chosen, it must be cost-effective. Federal-Mogul says a two-year payback is the longest operators will accept. There is no one ideal solution: trucks on urban work would benefit from engine downsizing through electric supercharging and efficient engine stop-start, while heavy long-haul trucks would benefit more from exhaust gas energy recovery, torque assistance and high-voltage dive to power accessories.
In all applications, care had to be taken to ensure gains made in one direction were not lost in another: for instance, diesel engines that did not work hard enough because of effective electrical assistance might struggle with emissions if the exhaust stream cooled.
Federal-Mogul also launched new diesel engine piston rings and bearing materials designed to cope with a new generation of fuel-saving ultra-low viscosity lubricants.
Although firmly rooted in diesel engines, Cummins has its eyes on a future that is at least partly electric, as evidenced by the recent acquisition of Johnson Matthey’s UK-based high-voltage battery business, and the previous takeover of low-voltage battery specialist Brammo.
The company said it was moving from diesel to a raft of solutions, with the most radical in evidence being the all-electric LF on the DAF stand at the show, for which Cummins had provided the complete electric powertrain.
Delphi, best-known in trucks as a fuel-injection supplier, has also a lot of expertise in the compact packaging of electronic control systems, which it anticipates applying to power electronics, particularly software, systems and system integration for hybrid drivelines. For instance if major modules can be integrated, then the need for runs of potentially dangerous high-voltage cables can be reduced.
The company expects it to be three-to-five years before the innovations that it is developing on the field appear on the market, with hybridisation to the fore. Full electrification will come much slower, with the first applications in urban deliveries.
Brake systems giant Wabco is looking at using trailer regenerative braking to help power trucks. Its e-Trailer sees an electric machine installed in the trailer’s third axle to recover brake energy and maintains that fuel savings of between 10 (long-haul) and 20 per cent (short-haul) will result if the energy harvested is then used to help propel the rig. Alternatively, it could be used to power a refrigeration unit. The system is two or three years away from market.
There is a penalty in payload and tyre wear on the rear axle is increased. However, Wabco argues that the European one-tonne payload allowance for hybrid trucks will offset the extra mass of the system, and tyre wear is traded against reduced wear on the trailer’s friction brakes. In any case, the massive investments made by truck manufacturers to reduce fuel consumption by just two or three per cent are dwarfed by the fuel savings that this system can yield.