Steel pistons. The switchover from one piston metal to another can upgrade performance and improve thermal dynamic efficiency. Combined with reduced friction losses due to the modified piston design (an important development target), steel-piston engines consume up to 4% less fuel, depending on operating conditions. A new steel piston for passenger car engines—some 8 years in development—by KS Kolbenschmidt is scheduled to go into series production at an OEM in 2014.

Besides friction improvements, the development efforts focused on noise reduction. To this end, the manufacturer conducted extensive NVH (noise, vibration, harshness) tests to optimize the design of the steel piston. One advantage of steel is its lower heat expansion and the resulting potential of having a significantly tighter clearance between the piston skirt and the cylinder bore.

As a consequence, there is an appreciable reduction in engine noise under cold, idling conditions—as determined by the piston contact changeover at the crankshaft angle of top dead center. The results of a dynamic simulation compared with an aluminum piston indicate a reduction of the acceleration level as an integral measure of vibration stimulation at the cylinder wall of more than 5 dB.

Cylinder vibration acceleration taking into account deformation. Click to enlarge.

Specifically on engines with aluminum blocks, the less favorable clearances on a warm engine at part load call for careful fine-tuning of noise level. With the aid of the optimized skirt stiffness combined with suitable piston pin offsetting and numerically optimized piston skirt profile, here, too, it is possible to achieve a level of steel piston acceleration on a par with an aluminum piston.

Over the past months, KSPG analyzed dynamic noise generation. Tests included revving up a cold engine at low load and analyzing cylinder wall acceleration at the pressure and counter-pressure sides. The results showed that at the 1–5 kilohertz frequency range of relevance to piston noise there was no structural acceleration of the engine block caused by the steel piston. Especially on the pressure side, it is evident that in this case the steel piston even has the edge over its aluminum cousin. Measurements carried out when revving up a warm engine under part load confirm likewise the successful optimization of the steel piston design since here, noise excitation caused by the steel piston is on a par with the aluminum variety.

Further extensive validation tests have, moreover, endorsed the fatigue strength of the steel piston as well as its compliance with required specifications regarding blow-by gas flow and oil consumption.

Comparison: aluminum and steel pistons revving up at low load and cold engine, structure-borne amplitudes and frequencies in the Campbell diagram. Click to enlarge.

Comparison: aluminum and steel pistons revving up at medium load and warm engine, structure-borne amplitudes and frequencies in the Campbell diagram. Click to enlarge.

Compact EGR valve enters series production. Pierburg GmbH has in recent years launched various exhaust gas recirculation (EGR) modules. A new generation of even more compact, even lighter EGR valves will be installed in all the diesel engines of a major German OEM beginning this fall.

In order to comply with the low Euro 6 diesel engine emission norms, additional measures are necessary for reducing emissions of nitrogen oxides (NO_x). One such measure is cooled exhaust gas recirculation. Such a system consists of a compact Pierburg EGR valve (cEM EGR), an EGR cooler, a bypass with a flap operated by a vacuum actuator, an EGR intake pipe that is directly fastened to the exhaust manifold, and an EGR exhaust pipe.

The cEM EGR valve is a so-called “hot mount,” able to withstand exhaust gas temperatures of up to 800 °C. In order to survive such heat, the valve is water-cooled by the cooling unit. The cEM EGR valve serves to precisely control the recirculated mass of exhaust gases. An electric motor controls the valve setting, between shut and open. The unit’s small footprint allows it to be mounted directly in the cooler module.

In order to permit the passage of high mass flow rates, the EGR valve opens in the direction of the exhaust gases. A contactless sensor determines the position. Another advantage is direct position identification with the aid of a sensor magnet on the valve rod for more precise control of the recirculated exhaust gases. With a powerful actuator, this is also able to tightly seal off for brief periods exhaust gas pressures of up to 5 bar.

Range extender. KSPG also showcased its 0.8-liter two-cylinder range extender (earlier post), which made its debut in Detroit at the 2012 show. The KSPG power unit consists of a V-type gasoline engine with a vertically positioned crankshaft and two generators with gear wheel drive. Except for the fuel tank and the radiator, all components are mounted on a ready-to-install support frame.

The Euro-6-rated port fuel injected engine has a power rating of 30 kW (40 hp) @ 4,500 rpm and torque of 66 N·m (49 lb-ft) @ 3,500 rpm.

The vertical crankshaft requires only a short construction height, such that the module can be integrated beneath the floor of a small passenger vehicle or, for example, be tucked neatly within a spare wheel recess. This installation option offers the easiest and least expensive modification procedure relative to conventional vehicle construction and leaves room for attractive compact-vehicle packaging and styling options.

The power unit is conceived in such a way that the vehicle interfaces are reduced to a minimum. Vehicle integration thus proves comparatively unproblematic and installation or disassembly can be performed easily and efficiently. This enables the range extender to be reduced to an additional accessory equipment option. The automobile can thus be delivered with or without a range extender, thus allowing for a strategy of modularity.