Engineering news
A team of researchers at EMPA, the Swiss Federal Laboratories for Materials Science and Technology, have been trying to improve the ‘respiratory organ’ of the combustion engine, which manages the aspiration of fresh air and the discharge of exhaust gases.
Today, mechanically driven camshafts are used to achieve this in production engines, with the help of additional complex mechanisms that allow the movement pattern given by the camshaft to be modified.
However, these aren’t as flexible as they could be, and engine-makers have long desired technology that can adapt to changing fuel properties and make fast valve movements at low speeds, as well as stroke adaptations and cylinder-selective widely variable valve timing.
To achieve this, the researchers – led by Patrik Soltic and his team at EMPA’s Automotive Powertrain Technologies laboratory – developed an electro-hydraulic valve train, which is actuated hydraulically and controlled electrically via a solenoid coil.
When a control current flows, a hydraulic valve opens allowing fluid to open the gas exchange valve to the desired extent in milliseconds. When the current is switched off, the valve is closed by a spring, and this movement feeds the energy required for opening the valve back into the system. This method requires significantly lower energy over a wide operating range compared to camshaft-driven systems.
The fuel consumption of a test spark-ignition engine from a 1.4-litre Volkswagen car was about 20 per cent lower than with conventional valve control in the low load range typical for passenger cars.
But the main advantage of the system is its flexibility. Opening and closing times and valve lift for each cylinder can be chosen completely unrestricted, so the engine operating condition can be varied from cycle to cycle, for example by intelligent load control, exhaust gas recirculation, or by deactivating unneeded cylinders without the driver noticing.
This means the engine is highly adaptable to new renewable fuels such as methanol or ethanol, which allow more residual gas to remain in the cylinder. Natural gas, biogas and syngas could also be used, and alternative combustion concepts can be implemented. Instead of oil, the system uses a mixture of water and glycol – engine coolant – as its hydraulic fluid.