MAHLE CamInCam®—variable valve train increases torque significantly
Stuttgart, September 2011—In the variable CamInCam® camshaft from MAHLE, the cams are rotated relative to each other as needed. MAHLE uses this technology to vary the effective opening time of the exhaust valves. The advantages can be observed in the torque curve, power output, emissions, and fuel economy of the engine.
The decisive advantage that the CamInCam® camshaft has over other variable valve train systems is that it can be installed within the same space constraints as a conventional camshaft. It is practically two camshafts in one. Which is due to its construction. There is an outer shaft and an inner shaft, arranged concentrically to each other. As part of the MAHLE process, the individual components are fully machined and then mounted on the camshaft. Depending on the operating point, the shafts—and thus the cams—are rotated relative to each other in order to achieve the optimal valve control strategy. Since the package constraint is the same, the CamInCam® camshaft can be used as a direct replacement for the ordinary camshaft. The engine manufacturer can therefore use the identical engine design for different performance versions.
Conventional camshafts, with their fixed opening times for the intake and exhaust valves, always represent a compromise between torque, power output, and fuel economy. Depending on the operating point, different cam profiles would be ideal on the exhaust side. Under full load at high speed, wide cam profiles are advantageous, which cause the exhaust valves to remain open for a long time. Flushing out the exhaust gases from the cylinder is improved, keeping the gas exchange work at a low level. This results in better fuel economy. At low speeds, narrow cam profiles are more suitable. This prevents the exhaust valves on different cylinders from being open at the same time. The backpressure in the exhaust manifold from the exhaust gas exiting one cylinder does not impede scavenging of the other cylinders. It also prevents crosstalk between adjacent cylinders through the exhaust manifold, which significantly reduces knocking tendency.
This compromise between an optimal cam profile for high torque at low speeds or for low consumption at rated speed is no longer relevant with the MAHLE CamInCam® camshaft.
For engines with a cam in block configuration (OHV), the MAHLE CamInCam® has been in series production since 2007, and is the only variable valve train system in the world for this configuration.
The CamInCam® technology shows its full potential in DOHC engines, with two overhead camshafts. In a four-cylinder gasoline engine with turbocharging and direct injection, it provides more torque at the low end under full load, and better transient response of the turbocharger.
At first, the MAHLE CamInCam® generates the required pressure gradient between the intake and exhaust sides with short exhaust valve opening times. The intake valves are then opened while the exhaust valves are still open. In this valve overlap phase, fresh air flows through the combustion chamber and enters the exhaust manifold. This effect has several advantages: First, the fresh air flushes the residual combustion gases out of the cylinder (scavenging), so that there is more oxygen in the combustion chamber for the next cycle, providing greater torque. Second, the fresh air further cools the combustion chamber. The air also helps to burn off residual fuel in the exhaust as it flows through, which results in lower emissions values. Finally, the turbocharger is now driven by the flowing fresh air in addition to the exhaust gas. At lower speeds, this increases torque, and "turbo lag" is eliminated.
Under full load at high speeds, the longer opening time can be set by rotating the cams relative to each other. The exhaust purge work, and thus fuel consumption and CO2 emissions, are reduced.
The MAHLE Group is one of the 30 largest companies in the automotive supply industry worldwide. With its two business units Engine Systems and Components and Filtration and Engine Peripherals, MAHLE ranks among the top three systems suppliers worldwide for piston systems, cylinder components, as well as valve train, air management, and liquid management systems. The Industry business unit bundles the MAHLE Group's industrial activities. These include the areas of large engines, industrial filtration, as well as cooling and air-conditioning systems. The Aftermarket business unit serves the independent spare parts market with MAHLE products in OE quality. In 2010, the MAHLE Group achieved sales of approximately EUR 5.3 billion (USD 7 billion); more than 47,000 employees work at over 100 production plants and eight research and development centers.