Servicing feature
The electromechanical camshaft phasing unit developed and produced by Schaeffler is about to be used for the first time in volume production in a series of Japanese engines.
The use of electromechanical phasing units instead of the current standard hydraulic systems allow the camshaft to adjust more quickly and accurately to the prevailing engine operating conditions. This reduces consumption and harmful emissions whilst simultaneously increasing comfort during stop/start operation.
There has been a boom in camshaft phasing systems in recent years. They control the timing for opening and closing the valves in the engine for optimum phasing of the intake/exhaust cycle in the cylinder with the engine speed and the torque demands.
Previously used only in very high-performance engines, variable opening and closing for inlet valves is now standard technology in modern petrol engines. Camshaft phasing systems are now also being used more frequently on the outlet side as well as, occasionally, in diesel engines. Until now, nearly all phasing units have been using hydraulic systems for the phasing.
Electromechanics make it possible to phase the camshaft at speeds up to 600 crank angle degrees per second. Hydraulic systems operate from two to ten times more slowly, irrespective of the engine speed and temperature. The increased dynamics of electromechanical phasing units allow very fast reactions to changes in load, even at low engine speeds, such as when the driver suddenly kicks down on the gas pedal while the engine is overrunning.
Unlike hydraulic systems, the reaction speed to a change in load is not dependent on the oil supply. In some cases, it is no longer necessary to have a larger engine oil pump which results in improvements in consumption.
Also, starting and stopping the engine is much smoother with electromechanical camshaft phasing units. This is important not only in stop/start operation but above all for hybrid vehicles. It is possible to start the internal combustion engine without any noticeable judder because, up to 200 rpm, the engine runs with reduced compression.
This is possible because the camshaft can be positioned as required before the engine starts. During acceleration, valve control times are synchronised with the injection so that there is a soft onset of compression; when compression and ignition are correctly adjusted, the result is smooth engine startup.
In design terms, Schaeffler aspires to a very compact solution consisting of a brushless DC motor and a gear unit with a high reduction ratio. The gear unit is based on a flexible toothed belt with an oval rolling bearing. It translates the engine speed at a ratio of approximately 70:1.
“We therefore achieve a very good balance between the size of the electric motor and the phasing speed,“explains Martin Scheidt, engine systems development manager at Schaeffler.
“And our gear units also operate completely silently.“Due to its compact design, the electromechanical camshaft phasing unit from Schaeffler occupies the same amount of space as the hydraulic system.
The electric motor used also contributes to the phasing accuracy as it serves not only as an actuator but also as a sensor. In addition to the position recognition already in use with hydraulic systems, usually four times per camshaft rotation, in the electrical system, the rotor position is checked continuously by integral sensors and assessed by an electronic control system.
The precise position of the camshaft is therefore always known. Schaeffler has developed the DC motor in house. “We could not find any motors on the market which satisfied our requirements for accuracy and durability,“says Scheidt, justifying the decision.
The electromechanical camshaft phasing unit developed and produced by Schaeffler is about to be used for the first time in volume production in a series of Japanese engines.
At the same time, the automotive supplier is also making further improvements to the hydraulic phasing units currently in extensive use in the market. With an annual production of 15 million phasing units, Schaeffler is one of the leading suppliers in this field. The trend is towards a central valve phasing system which can reach higher phasing speeds with less oil.
“Overall, we can see a clear trend to highly versatile valve trains,“says Scheidt. “The strict CO2 regulations mean that more and more automotive manufacturers are using cylinder deactivation systems.“In order to meet the demands of different customers, Schaeffler is developing a range of technologies from switchable roller finger followers to the fully variable electrohydraulic “UniAir“system which allow stepless variation of the valve lift.